Silicon is the main element of most die-cast aluminum alloys. It can improve the casting performance of the alloy, and its content is generally 7%-11%.
Improve the high temperature fluidity of the alloy
Reduce hot cracking tendency
Improve wear resistance
However, when the silicon content exceeds 12%, silicon and aluminum form a hypereutectic, and when there are many impurities such as copper and iron, hard spots of free silicon appear, which makes cutting difficult, and high-silicon aluminum alloys will corrode the casting crucible The effect is serious.
The copper content in the alloy is usually 2.5% ~ 5%. Increasing the copper content can improve the fluidity, tensile strength and hardness of the alloy, but reduce the corrosion resistance and plasticity, and increase the tendency of hot cracking.
Adding a small amount (about 0.2-0.3%) of magnesium to high-silicon aluminum alloy can increase the strength and yield limit, and improve the machinability of the alloy.
If the magnesium content is too high, the casting performance will be poor, the strength and plasticity at high temperature will be low, and the shrinkage will be large during cooling, so it is easy to produce hot cracks and form porosity.
Zinc in the aluminum-zinc-based aluminum alloy can improve fluidity, improve casting performance, and increase tensile strength, but the tendency of hot cracking increases and the corrosion resistance decreases, generally less than 1.2%.
Since the adhesion of aluminum alloy to the mold is very strong, it is especially strong when the iron content is below 0.6%. When it exceeds 0.6%, the sticking phenomenon is greatly reduced, so the iron content should generally be controlled within the range of 0.6 to 1%, which is good for die casting.
When the iron content is too high, the iron exists in the alloy as a flake or needle-like structure of FeAl3, Fe2Al7 and Al-Si-Fe, which reduces mechanical properties. This structure will also reduce the fluidity of the alloy and increase the hot cracking property. Large, the corrosion resistance is reduced.
Manganese in aluminum alloys can reduce the harmful effects of iron, and can make the flake or needle-like structure formed by iron in the aluminum alloy become a fine crystal structure. Therefore, generally aluminum alloys allow the presence of less than 0.5% manganese. When the manganese content is too high, it will cause segregation, and the manganese content is generally controlled below 0.6%.
Nickel in aluminum alloy can increase the strength and hardness of the alloy and reduce the corrosion resistance. Nickel has the same effect as iron, which can reduce the corrosion of the alloy to the mold, and at the same time, it can neutralize the harmful effects of iron and improve the welding performance of the alloy. When the nickel content is between 1 and 1.5%, the casting can obtain a smooth surface after polishing. Due to the lack of nickel sources, nickel-containing aluminum alloys should be used as little as possible.
From the above we can see that most alloying elements have their positive and negative effects. One depends on the quantity, and the other depends on who you match with. As the ancients said, "things have no beauty or evil, and passing is a disaster."