1. 1 × × × represents pure aluminum series with 99% or more; 2 × × represents aluminum-copper Alloy series; 3 × represents aluminum-manganese Alloy series; 4 × Represents aluminum-silicon Alloy series; 5 × Represents aluminum-magnesium Alloy series; 6 × Represents aluminum-magnesium-silicon Alloy series; 7 × × × represents a series of al-zn alloys and 8 × × represents a system of alloys other than the above mentioned.

2. 1 × × ×  system aluminum alloy is a commercial pure aluminum, which has the characteristics of small density, good conductivity, high heat conduction, large latent heat of melting, large light reflection coefficient, small interface area of thermal neutron absorption and beautiful appearance. Aluminum has good corrosion resistance because it can form dense and strong oxide film on the surface of aluminum in air, which can prevent the invasion of oxygen. 1 × × × system aluminum alloy can not be strengthened by heat treatment, but can be strengthened by cold work hardening, so its strength is low.

2 × × × 

 2 × × × aluminum alloy is usually called duralumin alloy because of its high strength, good heat resistance and machinability, but poor corrosion resistance, and intergranular corrosion under certain conditions, or a layer of core plate has electrochemical protection of 6 × × × series aluminum alloy, in order to greatly improve its corrosion resistance. Among them, Al-Cu-Mg-Fe-Ni Alloy has a very complex chemical composition and phase composition, it has high strength at high temperature, and has good processing properties. It is mainly used for forging heat-resistant parts under 150 ~ 250 °C Although the strength of Al-Cu-Mn alloy is lower than that of Al-Cu-Mg alloy 2A12 and 2A14 at room temperature, the strength of Al-Cu-Mn Alloy is higher than that of Al-Cu-Mg alloy at 225ー250 °C or higher, mainly used in heat-resistant weldable structural parts and forgings. The alloys are widely used in the fields of aeronautics and astronautics.

3 × × × . It has high plasticity, good welding performance, higher strength than 1 × × × aluminum alloy, and corrosion resistance is similar to 1 × × × aluminum alloy. It is a medium strength aluminum alloy with good corrosion resistance.

4 × × ×  As well as with heat treatment strengthened alloy after welding absorbed some elements, can be strengthened through heat treatment. Because of its high silicon content, low melting point, good melt fluidity, easy retraction and no Brittleness of the final product, the alloy is mainly used to make aluminum alloy welding additive materials, such as Brazing Plate, welding rod and welding wire, etc. . In addition, due to the wear resistance and high temperature performance of some of the alloys are also used to manufacture Pistons and heat-resistant parts. The alloy containing about 5% W (SI) is black-gray after anodizing, so it is suitable for building materials and decorative parts.

5 × × × . The alloy has low density, higher strength than 1 × × × and 3 × × × × , middle and high strength, good fatigue property and welding property, good corrosion resistance in marine atmosphere. In order to avoid stress corrosion of high magnesium alloy, the final cold-worked products should be stabilized or the final cold-worked amount should be controlled, the service temperature is limited (not more than 65 °C) . The alloy is mainly used for making welded structural parts and for ship applications.

6 × × × × 

6 × × × aluminum alloy is an aluminum alloy with magnesium and silicon as main alloy elements and Mg2si as strengthening phase. The alloy has the advantages of medium strength, high corrosion resistance, no tendency of stress corrosion cracking, good weldability, invariable corrosion property of welding zone, good formability and technological property. When copper is contained in the alloy, the strength of the alloy is close to that of the 2 × × × aluminum alloy, the processing property is better than that of the 2 × × aluminum alloy, but the corrosion resistance is poor, and the alloy has good forging property. The most widely used alloys are 6061 and 6063, which have the best comprehensive properties and economy. The main products are extruded profiles, which are the best extruded alloys.

7 × × × × series

 7 × × series aluminum alloy is an aluminum alloy with zinc as the main alloy element, which can be strengthened by heat treatment. Al-Zn-Mg alloy with magnesium in it has good hot deformation property, wide quenching range, high strength under proper heat treatment condition, good welding property and general corrosion resistance, has Certain Stress Corrosion tendency, is the high strength weldable aluminum alloy. Al-Zn-Mg-Cu alloy is developed on the basis of Al-Zn-Mg alloy by adding copper, its strength is higher than 2 × × × aluminum alloy, generally called super high strength aluminum alloy, its yield strength is close to tensile strength, yield strength ratio is high, specific strength is also very high, but the plastic and high-temperature strength is low, should be used at room temperature, below 120 °C load-bearing structural components, alloy easy processing, good corrosion resistance and high toughness. The alloys are widely used in aerospace and aviation fields and have become one of the most important structural materials in this field.

8 × × × × × 8 × × × series aluminum alloy is more commonly used for 8011 belongs to other series, most of them are used for aluminum foil, the production of aluminum bars is not commonly used. 3. Effect of alloying elements the major impurity elements in 1 × × ×  These micronutrient also act as alloying agents in some 1 × × × series aluminum alloys and have an effect on the microstructure and properties of the alloys. The electrical properties of 1 × × × system aluminum alloy are greatly affected by the addition of elements and impurities, and the electrical conductivity of 1 × × × system aluminum alloy is generally decreased, in which the decrease of nickel, copper, iron, zinc and silicon is less, but the decrease of vanadium, chromium, manganese and titanium is more. In addition, the existence of impurities will destroy the continuity of oxide film formed on the surface of aluminum, and reduce the corrosion resistance of aluminum.

Iron and aluminum can form FEAL3, iron and silicon and aluminum can form ternary compounds α (AL, Fe, SI) and β (AL, FE, SI) , which are the main phases in 1 × × × system aluminum alloys. They are hard and brittle, which have a great effect on mechanical properties, and the recrystallization temperature can be increased. Silicon and iron are coexisting elements in aluminum. When there is excess silicon, the alloy is hard and brittle, which increases the strength and decreases the plasticity of the alloy, and has obvious effect on the secondary recrystallization grain size of high purity aluminum. Cu mainly exists in solid solution state in 1 × × × aluminum alloy, which contributes to the strength of the alloy and affects the recrystallization temperature. MG AND MG can be added to 1 × × × aluminum alloy and exist mainly in solid solution state. The effect of MG AND MG is to increase strength and has little effect on recrystallization temperature. MN-MN can obviously increase the recrystallization temperature, but has little effect on grain refinement. The effect of CR on MN. TI-TI is the main modification element of 1 × × × aluminum alloy, which can refine the ingot grain, increase the recrystallization temperature and refine the grain. However, the effect of Ti on recrystallization temperature is related to the content of fe and Si, and the effect is very significant when fe is contained in the alloy. B Boron is also the main modification element of 1 × × × aluminum alloy, which can refine the ingot grain, increase the recrystallization temperature and refine the grain.

A small amount of Zn (W (Zn) = 0.1% ~ 0.5%) has little effect on the Mechanical Properties of Al-Cu-Mg Alloy at room temperature, but decreases the heat resistance of the alloy. W (Zn) in the alloy shall be limited to less than 0.3% . The main alloy grades of Al-Cu-Mg-Fe-Ni Alloy are 2A70,2A80,2A90, etc. . The effect of Cu content on the room temperature strength and heat resistance of Al-Cu-Mg-Fe-Ni Alloy is similar to that of al-Cu-mg Alloy. Because the copper content of the alloy is lower than that of Al-Cu-Mg alloy, the alloy is located in the α + s (Al2CuMg) two-phase zone, so the alloy has higher room temperature strength and good heat resistance, this is good for the heat resistance of the alloy. The effect of MG and MG content on the room temperature strength and heat resistance of the alloys is similar to that of al-cu-Mg alloy. Because the magnesium content of the alloy is lower than that of Al-Cu-Mg alloy, the alloy is located in α + s (Al2CuMg) two-phase zone, so the alloy has higher room temperature strength and good heat resistance. Ni and copper in the alloy can form insoluble ternary compound, the formation of AL3(Cuni)2 occurs when the nickel content is low (Alcuni) and high (Cuni) . Therefore, the presence of nickel can reduce the concentration of copper in the solid solution. When the iron content is very low, the increase of nickel content can reduce the hardness and the strengthening effect of the alloy.

Like nickel,When the nickel content is very low, the hardness of the alloy decreases obviously at the beginning with the increase of iron content, but increases again when the iron content reaches a certain value. When fe and Ni are added to AlCu2.2MG1.65 alloy at the same time, the hardness changes of the quenched natural aging, quenched artificial aging, quenched and annealed state are similar, accordingly, a minimum value of the lattice constant appears in the quenched state. Al7Cu2Fe phase occurs when the FE content is higher than the NI content. AlCuNi phase occurs when the nickel content is higher than the iron content. The presence of cu-containing ternary phase reduces the concentration of cu in the solid solution. In this case, because there is no excess iron or nickel to form the insoluble copper phase, the copper in the alloy not only forms the s (Al2CuMg) phase, but also increases the concentration of copper in the solid solution, which is beneficial to improving the strength and heat resistance of the alloy. The content of fe and NI can affect the heat resistance of the alloy. Al9FeNi phase is a hard brittle compound with very low solubility in Al. after forging and heat treatment, when they are dispersed in the microstructure, the heat resistance of the alloy can be improved remarkably. The addition of W (SI) = 0.5% ~ 1.2% in 2A80 alloy can increase the strength of the alloy at room temperature, but decrease the heat resistance of the alloy. The addition of w (TI) = 0.02% ~ 0.1% in Ti2A70 alloy can refine as-cast grains and improve forging properties, which is beneficial to heat resistance, but has little effect on room temperature properties.

The main grades of Al-Cu-Mn alloys are 2A16,2A17 and so on. Magnesium, titanium and zirconium are added to the alloys, while the main impurity elements are iron, silicon and zinc. The effects are as follows: Cu at room temperature and high temperature, the strength of the alloy increases with the increase of copper content. When W (Cu) reaches 5.0% , the strength of the alloy approaches the maximum value. In addition, copper can improve the weldability of the alloy. MN-MN is the main element to improve the heat-resistant alloy. It can increase the activation energy of atoms in solid solution and reduce the diffusion coefficient of solute atoms and the decomposition rate of solid solution. The formation and growth of precipitated t phase (Al20Cu2Mn3) is very slow when the solid solution is decomposed, so the properties of the alloy are stable when it is heated for a long time at a certain high temperature. Adding proper MN (W (MN) = 0.6% ~ 0.8%) can improve the room temperature strength and endurance strength of the alloy in quenching and natural aging state. However, if the content of MN is too high and the number of t phase increases, the interface will increase, the diffusion will be accelerated, and the heat resistance of the alloy will decrease. In addition, manganese can also reduce the tendency of the alloy to crack during welding. The 2A17 alloy was prepared by addition of MG (W (MG) = 0.25% ~ 0.45%) with constant cu and mn contents in 2A16 alloy. Magnesium can improve the strength of the alloy at room temperature and the heat resistance under 150 ~ 225 °C. However, when the temperature rises again, the strength of the alloy decreases obviously. However, the addition of MG can deteriorate the weldability of the alloy, so the impurity W (MG) & Lt; 0.05% is added to the heat-resistant weldable 2A16 alloy.

Ti can refine as-cast grains, increase the recrystallization temperature, decrease the decomposition tendency of supersaturated solid solution, and make the microstructure stable at high temperature. However, when w (TI) & GT; 0.3% , large needle-like crystals TiAl were formed, and the heat resistance of the alloy was decreased. The W (Ti) content of the alloy is 0.1% ~ 0.2% . When W (ZR) = 0.1% ~ 0.25% was added into 2219 alloy, the grain was refined, the recrystallization temperature and the stability of solid solution were increased, thus the heat resistance and the weldability and the plasticity of weld were improved. However, when w (Zr) is high, more brittle compounds ZRAL3 can be formed. When W (FE) & GT; 0.45% in Fe alloy, the insoluble phase Al7Cu2Fe can be formed, which can reduce the mechanical properties of the alloy during quenching and aging and the stress rupture strength at 300 °C. So W (FE) & Lt; 0.3% was restricted. A small amount of SI (W (SI) & LT; 0.4%) has no obvious effect on the mechanical properties at room temperature, but decreases the tensile strength at 300 °C and the mechanical properties at room temperature when w (SI) & GT; 0.4% . So W (SI) & Lt; 0.3% is restricted. A small amount of Zn (W (Zn) = 0.3%) has no effect on the room temperature properties of the alloy, but it can accelerate the diffusion rate of copper in aluminum and reduce the stress rupture strength of the alloy at 300 °C, thus limiting w (Zn) & Lt; 0.1% .

3 × × × alloy elements and impurity elements play important roles in 3 × × × Aluminum Alloy: Mn-Mn is the only main alloy element in 3 × × × aluminum alloy, its content is generally in the range of 1% ー1.6% , the strength, plasticity and technological properties of the alloy are good, mN AND AL can form MNAL6 phase. The strength of the alloy increases with the increase of MN content. When W (MN) & GT; 1.6% , the strength of the alloy increases, but the alloy is easy to crack during deformation due to the formation of a large amount of brittle compound MNAL6. With the increase of W (MN) , the recrystallization temperature of the alloy increases correspondingly. Due to the supercooling ability of the alloy, there is a great intragranular segregation during rapid cooling crystallization, and the concentration of manganese is low at the center of Dendrite, but high at the edge of DENDRITE, it is easy to form coarse grain after annealing.. W (FE) = 0.4% ~ 0.7% , but w (FE + MN) & Lt; 1.85% should be added to the alloy, which can effectively refine the grain after annealing, otherwise a large number of FeMn AL6 compounds will be formed, the mechanical properties and technological properties of the alloy will be significantly reduced. Si silicon is a harmful impurity. Si and MN form complex ternary phase t (Al12Mn3Si2) , which can also dissolve iron and form (AL, FE, MN, SI) quaternary phase. If fe and SI exist in the alloy at the same time, the α (Al12Fe3Si2) or β (Al9Fe2Si2) phase is formed first, which destroys the beneficial effect of fe. Therefore, W (SI) & LT; 0.6% should be controlled. Silicon can also reduce the solubility of manganese in aluminum, and has a greater effect than iron. Iron and silicon can accelerate the decomposition of manganese from supersaturated solid solution during thermal deformation and improve some mechanical properties. Mg a small amount of MG (W (MG)≈0.3%) can significantly refine the annealed grains and slightly increase the tensile strength of the alloy. But it also damages the surface gloss of the annealed material. Magnesium can also be an alloying element in Al-Mg alloys. The addition of W (MG) = 0.3% ~ 1.3% increases the strength and decreases the elongation (annealed state) of the alloys, so Al-Mg-mn alloys have been developed.

When W (CU) = 0.05% ~ 0.5% , the tensile strength of Cu alloy can be significantly increased. However, a small amount of copper (W (Cu) = 0.1%) can decrease the corrosion resistance of the alloy. Therefore, W (Cu) & Lt; 0.2% should be controlled. ZNW (Zn) & Lt; 0.5% has no obvious effect on the mechanical properties and corrosion resistance of the alloy. Considering the weldability of the alloy, W (ZN) & Lt; 0.2% is limited. 4 × × × alloy elements and impurity elements play important roles in 4 × × × Alloy: Si is the main alloy component in the alloy, the content of SI is 4.5% ~ 13.5% , SI exists in the form of α + SI eutectic and β (Al5FeSi) , the content of SI increases, with the increase of EUTECTIC, the fluidity of the alloy melt increases, and the strength and wear resistance of the alloy also increase. Ni-ni can form intermetallic compounds insoluble in aluminum, which can improve the high temperature strength and hardness of the alloy without reducing its linear expansion coefficient. Effect of Fe on NI. CU-CU can form CUAL2 and s phase, which can improve the strength of the alloy. MG AND MG can form MG2SI and s phase, which can improve the strength of the alloy. CR-CR can refine the grains and improve the air tightness of the alloy. Effect of Ti on CR.

5 × × × . The specific effects are as follows: MG-MG mainly exists in solid solution state and β (Mg2Al3 or Mg5Al8) phase. Although the solubility of MG in the alloy decreases rapidly with the decrease of temperature, it is difficult to form nuclei due to precipitation, with few cores and large precipitates, as a result, the aging strengthening effect of the alloy is low, and it is usually used in annealing or cold working state. Therefore, this series of alloy is also called non-reinforced aluminum alloy. The strength of the alloy increases with the increase of MG content, but the plasticity decreases, and the processing properties become worse. The effect of MG content on the recrystallization temperature of the alloy was significant. When W (MG) & LT; 5% , the recrystallization temperature decreased with the increase of MG content, and when W (MG) & GT; 5% , the recrystallization temperature increased with the increase of MG content. When W (MG) & LT; 6% , the tendency of weld crack decreases with the increase of MG content, but the reverse is true when W (MG) & GT; 6% ; when w (MG) & LT; 9% , when the content of magnesium is more than 9% , the strength, plasticity and Welding Coefficient of the weld are obviously decreased, but the change is not obvious.

CR-CR and MN have similar effects, which can increase the strength of Base metal and weld, reduce the tendency of hot cracking and improve the resistance to stress corrosion, but make the plasticity slightly lower. Chromium can be substituted for Manganese in some alloys. As far as strengthening effect is concerned, chromium is inferior to manganese, if two elements are added at the same time, its effect is bigger than the single addition. The addition of trace beryllium (W (B E) = 0.0001% ~ 0.005%) to Be in high magnesium alloy can reduce the tendency of cracks in Ingot, improve the surface quality of rolled sheet and reduce the burning loss of magnesium during melting, it also reduces the oxide formed on the surface of the material during the heating process. A small amount of titanium is added to Ti-high magnesium alloy, which is mainly used to refine the grains. Fe-Fe-Fe, MN and CR can form insoluble compounds, which can reduce the effect of MN and CR in the alloy. In addition, iron will reduce the corrosion resistance of the alloy, so generally control W (FE) & Lt; 0.4% , for welding wire material it is best to limit W (FE) & LT; 0.2% . Si is a harmful impurity (except 5A03 alloy) . Si and MG FORM MG2SI phase. Because of the excess MG content, the solubility of Mg2Si phase in the Matrix is decreased, so the strengthening effect is not obvious and the plasticity of the alloy is reduced. During rolling, silicon has more negative effect than iron, so W (SI) & Lt; 0.5% should be restricted. 5A03 alloy W (SI) = 0.5% ~ 0.8% can reduce the tendency of welding crack and improve the welding property of the alloy.

The corrosion resistance of the alloy will be worse when Cu is small, so w (Cu) & Lt; 0.2% should be restricted, and some alloys should be restricted more strictly. ZNW (Zn) & Lt; 0.2% has no obvious effect on the mechanical properties and corrosion resistance of the alloy. The tensile strength of high magnesium alloy can be increased by 10 ~ 20MPa by adding a small amount of zinc. The Impurity W (Zn) & LT; 0.2% should be limited. The NA trace impurity sodium can strongly damage the hot deformation property of the alloy, and the NA Brittleness appears, which is more prominent in the high mg alloy. The way to eliminate the sodium Brittleness is to change the free sodium enriched in the grain boundary into compound, which can be produced by chlorination and discharged with slag, or by adding trace antimony. 

6 × × ×

The main alloy elements of the 6 × × × aluminum alloy are magnesium, silicon and copper, the micronutrient elements of the alloy are manganese, chromium and titanium, and the impurity elements are mainly iron and zinc, the effect is as follows: The change of MG, MG and SI content has no obvious effect on the tensile strength and elongation of al-Mg-si Alloy in annealed state. With the increase of MG and SI contents, the tensile strength and elongation of Al-Mg-Si Alloy in natural aging state increased. When the total content of MG and SI is fixed, the ratio of MG and SI content also has great influence on the properties. The tensile strength of the alloy increases with the increase of SI content. When the content of Mg2Si phase is fixed and the silicon content is increased, the strengthening effect and the elongation of the alloy are improved slightly. The tensile strength of the alloy increases with the increase of MG content. The maximum tensile strength of the alloy with small SI content lies in the three-phase region of α (AL)-mg2si-mg2al3. The maximum tensile strength of Al-Mg-Si ternary alloy lies in the triphase region of α (AL)-MG2SI-SI. The effect of magnesium and silicon on the mechanical properties of the alloy in the quenched artificially aged state is basically the same as that in the quenched naturally aged state, but the tensile strength is greatly improved, and the maximum value is still within the α (Al)-MG2SI-SI three-phase zone, at the same time, the elongation rate decreased correspondingly. The corrosion resistance decreases with the increase of the amount of residual SI and Mg2si in the alloy. When the alloy lies in the α (AL)-MG2SI two-phase region and MG2SI phase all dissolve in the single-phase region of the Matrix, the corrosion resistance of the alloy is the best. All the alloys have no tendency of stress corrosion cracking. However, in the α (AL)-MG2SI two-phase zone, W (SI) = 0.2% ー0.4% , W (MG) = 1.2% ー1.4% and in the α (Al)-MG2SI-SI three-phase zone, W (SI) = 1.2% ー2.0% , W (MG) = 0.8% ー2.0% , the tendency of welding crack is small. For Si, see description of the action of MG. The existence of copper in the microstructure of CuAl-Mg-Si alloy depends not only on the content of copper, but also on the content of magnesium and silicon.

For Si, see description of the action of MG. The existence of copper in the microstructure of CuAl-Mg-Si alloy depends not only on the content of copper, but also on the content of magnesium and silicon. When the content of copper is small, and the ratio of W (MG) to w (SI) is 1.73:1, Mg2Si phase copper is dissolved in the Matrix, when the content of copper is large, and the ratio of w (MG) to w (SI) is less than 1.08, a phase of w (Al4CuMg5Si4) may be formed, and the remaining copper forms CUAL2, w (MG) : When the ratio of W (SI) is greater than 1.73, s (Al2CuMg) and CuAl2 phase may be formed. W phase is different from s phase, CuAl2 phase and MG2SI phase. In solid state, only partial dissolution takes part in strengthening, and the strengthening effect is not as great as that of Mg2Si phase. The addition of copper in the alloy not only improves the plasticity of the alloy during hot working, but also increases the strengthening effect of heat treatment, restrains the extrusion effect and reduces the anisotropy of the alloy after adding manganese. Manganese can improve the strength, corrosion resistance, impact toughness and bending properties of MN alloy. When W (MN) & Lt; 0.2% was added to almg 0.7si 1.0 alloy, the strength of the alloy increased greatly with the increase of MN content. With the increase of MN content, MN and SI form AlMnSi phase, losing some SI which is necessary to form Mg2si phase, and the strengthening effect of AlMnSi phase is less than that of MG2SI phase. Therefore, the strengthening effect of the alloy decreases. When manganese and copper are added at the same time, the strengthening effect is not as good as adding manganese alone, but the elongation is increased and the grain size of annealed products is improved.

When manganese is added into the alloy, the serious intragranular segregation of manganese in the α phase will affect the recrystallization process of the alloy and result in the grain coarsening of the annealed products. In order to obtain fine grain materials, the INGOT must be homogenized at high temperature (550 °C) to eliminate manganese segregation. It is better to heat up quickly when annealing. Chromium and manganese have similar effects. Chromium can inhibit the precipitation of Mg2Si phase at grain boundary, delay the natural aging process and increase the strength after artificial aging. Chromium can refine the grain and make the grain after recrystallization appear elongated, so the corrosion resistance of the alloy can be improved. The suitable W (CR) = 0.15% ~ 0.3% . The addition of w (TI) = 0.02% ~ 0.1% and W (CR) = 0.01% ~ 0.2% in TI6 × × × aluminum alloy can reduce the columnar grain structure of Ingot, improve the forging property of alloy and refine the grain size of products. Fe containing a small amount of Fe (W (FE) & Lt; 0.4%) has no bad effect on the mechanical properties and can refine the grains. When W (FE) & GT; 0.7% , the insoluble (ALMNFESI) phase will decrease the strength, plasticity and corrosion resistance of the product. When iron is contained in the alloy, the color of the product surface after anodizing treatment will become bad. A small amount of Zn impurity has little effect on the strength of the alloy, W (Zn) & Lt; 0.3% . 7 × × × system Al-Zn-Mg Alloy Al-Zn-Mg alloy, in which zn and mg are the main alloying elements, the mass fraction is generally less than 7.5% . The tensile strength and heat treatment effect of the alloy increase with the increase of zn and MG content.

The Stress Corrosion tendency of the alloy is related to the sum of zinc and magnesium contents. The alloy with high magnesium and low zinc or high zinc and low magnesium has good stress corrosion resistance as long as the sum of zinc and magnesium does not exceed 7% . The tendency of weld crack decreases with the increase of MG content. Manganese, chromium, copper, zirconium and titanium are the main micronutrient elements in Al-Zn-Mg alloys, and iron and silicon are the main impurity elements. The specific effects are as follows: MN and chromium can improve the stress corrosion resistance of Al-Zn-Mg alloys, W (MN) = 0.2% ~ 0.4% , the effect is remarkable. The effect of adding chromium is bigger than adding manganese. If adding manganese and chromium at the same time, the effect of Reducing Stress Corrosion tendency is better. W (CR) = 0.1% ~ 0.2% is suitable. Description of the action of MN ELEMENT IN CR. ZR-ZR can significantly improve the weldability of Al-Zn-Mg alloys. When 0.2% zr is added into AlZn5Mg3Cu0.35C0.35 alloy, the welding crack decreases obviously. Zirconium can also increase the recrystallization end temperature of the alloy. In alzn4.5 MG1.8 MN0.6 alloy, when W (Zr) & GT; 0.2% , the recrystallization terminal temperature of the alloy is above 500 °C, so the deformed structure is retained after quenching. The addition of w (ZR) = 0.1% ~ 0.2% to Al-Zn-Mg alloy containing mn can also improve the stress corrosion resistance of the alloy, but the effect of Zr is lower than that of CR. Ti can refine the grains of as-cast Ti alloy and improve the weldability of the alloy, but the effect is lower than that of zirconium. Better if titanium and zirconium are added at the same time. When W (TI) = 0.12% AlZn5Mg3Cr0.3CU0.3 alloy, W (Zr) & GT; 0.15% , the weldability and elongation of the alloy are better than that of the alloy added W (Zr) & GT; 0.2% . Titanium can also increase the recrystallization temperature of the alloy. CuAl-Zn-Mg alloys with a small amount of copper can improve the stress corrosion resistance and tensile strength, but the solderability of the alloys is reduced. FE-FE can reduce the corrosion resistance and mechanical properties of the alloy, especially for the alloy with high MN content. Therefore, the iron content should be as low as possible, W (FE) & Lt; 0.3% should be limited. SI-SI can decrease the strength of the alloy, decrease the bending property slightly and increase the tendency of welding crack. W (SI) & LT; 0.3% should be limited.

Al-Zn-Mg-Cu Alloy Al-Zn-Mg-Cu alloy can be strengthened by heat treatment, the main strengthening elements are zinc and magnesium, copper also has some strengthening effect, but its main role is to improve the corrosion resistance of the material. A small amount of manganese, chromium, zirconium, vanadium, titanium and Boron are also found in the alloy. Iron and silicon are harmful impurities in the alloy. The interaction between them is as follows: MG, Zn and MG are the main strengthening elements. When they exist together, η (MgZn2) and t (Al2Mg2Zn3) phases can be formed. The solubility of η phase and t phase in aluminum is very large, and the solubility of MgZn2 is 28% at eutectic temperature and 4% ー5% at room temperature, the increase of zinc and magnesium content can increase the strength and hardness greatly, but decrease the plasticity, stress corrosion resistance and fracture toughness.

The description of the action of MG element can be found in Zn. Cu, when w (Zn) : W (MG) & GT; 2.2, and the content of copper is higher than the ferritic content, Cu and other elements can produce a strengthening phase s (CuMgAl2) , which can increase the strength of the alloy, but the possibility of the existence of s phase is very small under the contrary condition. Copper can reduce the potential difference between grain boundary and grain boundary, change the structure of precipitates and refine grain boundary precipitates, but it has little effect on the width of PFZ. However, when w (Cu) is about 3% , the corrosion resistance of the alloy deteriorates. Copper can increase the supersaturation degree of the alloy, accelerate the aging process at 100 ~ 200 °C, expand the stable temperature range of GP zone, and improve the tensile strength, plasticity and fatigue strength. In addition, the U. S. E. S. Lin Et Al. investigated the effect of copper content on the fatigue strength of 7 × × × aluminum alloy. It was found that the cyclic strain fatigue resistance and fracture toughness increased with the increase of copper content in a small range, the etching rate is reduced in the etching medium, but the addition of copper tends to produce intergranular corrosion and pitting corrosion. The effect of copper on fracture toughness is related to the value of W (Zn) : W (MG) . When the ratio is small, the higher the content of copper, the worse the toughness.

B is the same as Ti. Fe, FE, Fe, Fe, Fe and SI are unavoidable harmful impurities in 7 × × × aluminum alloys, which come from raw materials, tools and equipments used in melting and casting. These impurities are mainly in the form of hard and brittle FEAL3 and free silicon, and they are also associated with the formation of large compounds such as MN, CR (FeMn) AL6, (FeMn) NCR Si2Al5 and AL (FeMn) . FEAL3 has the effect of refining grain size, but has a greater effect on corrosion resistance, with the increase of insoluble phase content, the volume fraction of insoluble phase also increases. These insoluble second phases will break up and elongate when they are deformed, consisting of short, disconnected strips. Because the impurity particles are distributed in the grain or grain boundary, when plastic deformation, some pores occur on the grain-matrix boundary and micro-cracks occur, which become the origin of macro-cracks, and at the same time, it will promote the premature development of cracks. In addition, it has a great influence on the growth speed of fatigue crack, and it can reduce the local plasticity when it is damaged, which may be related to the shortening of the distance between particles due to the increase of the impurity quantity, thereby reducing the plastic deformation around the crack tip associated with the flow. Because the phase containing fe and SI is difficult to dissolve at room temperature, it plays the role of notch and is easy to become the source of crack and cause the material to break. Therefore, the content of iron and silicon is strictly controlled in the design and production of the new alloy. In addition to using high-purity metal materials, some measures are taken in the melting and casting process to prevent the two elements from being mixed into the alloy. For Si, see the description of the action of Fe. 

Source: Caitong