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Alloy composition, effective alloying elements: aluminum, copper, magnesium; harmful impurities: lead, cadmium, tin, iron.
Function: ①Improve the casting performance of the alloy, increase the mobility of the alloy, refine the grains, and cause
solid solution strengthening, Improve mechanical performance.
②Reduce the ability of zinc to iron and reduce the corrosion of iron materials such as gooseneck, mold and crucible.
The aluminum content is controlled at 3.8 to 4.3%. Mainly considering the required strength and fluidity, good fluidity is a necessary condition for obtaining a complete, accurate size and smooth surface casting.
The influence of aluminum on fluidity and mechanical properties is shown in Figure 1. The fluidity reaches its maximum when the aluminum content is 5%; it drops to the minimum of 3%. The influence of aluminum on impact strength is shown in Figure 1. The impact strength reaches the maximum when the aluminum content reaches 3.5%; the minimum is 6%. The aluminum content is greater than 4.3%, and the alloy is brittle. The aluminum content is below the specified range, making it difficult to fill thin-walled parts, and casting cracks may occur after cooling. The adverse effect of aluminum in zinc alloys is the generation of Fe2Al3 dross, which causes its content to decrease.
Function: 1. Improve the hardness and strength of the alloy;
2. Improve the wear resistance of the alloy;
3. Reduce intergranular corrosion.
Disadvantages: 1. The copper content is greater than 1.25%, which will cause the die size and mechanical strength to change due to aging;
2. Reduce the ductility of the alloy.
Effect: ①The effect of increasing the copper content on the strength of the alloy is shown in Figure 4.
Function: ①Reduce intergranular corrosion
②Refine the alloy structure, thereby increasing the strength of the alloy
③ Improve the wear resistance of the alloy
Unfavorable: ①Mg content> 0.08%, leading to hot embrittlement, reduced toughness, and reduced fluidity.
②Prone to oxidation loss of alloy melt.
The influence of magnesium on alloy fluidity is shown in Figure 1.
(4) Impurity elements: lead, cadmium, tin
make the intergranular corrosion of zinc alloy become very sensitive, accelerate its own intergranular corrosion under the environment of temperature and humidity, reduce Mechanical properties, resulting in dimensional changes of castings.
When the zinc alloy impurity elements lead and cadmium content are too high, the workpiece is just die-cast and the surface quality is normal, but after storing at room temperature for a period of time (eight weeks to several months), the surface foams.
(5) Impurity element: iron
① Iron and aluminum react to form Al5Fe2 intermetallic compound, which leads to the loss of aluminum and the formation of dross.
②The formation of hard spots in die-casting affects processing and polishing.
③Increase the brittleness of the alloy.
The solubility of iron in the zinc solution increases with the increase in temperature, and the temperature change of the zinc solution in each furnace will result in iron (when the temperature decreases) or unsaturation ( When the temperature rises) supersaturation. When the iron element is supersaturated, the supersaturated iron will react with the aluminum in the alloy, resulting in an increase in pollution. When the iron element is not saturated, the corrosion of the alloy and gooseneck material on the zinc pan will increase and return to saturation. The common result of the two temperature changes is the result of the consumption of aluminum, which leads to more scum.
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