1 Casting performance. Used as a low-aluminum content zinc alloy for die casting, the composition is near the eutectic point, the solidification temperature range is small, the melting temperature is low, and the fluidity is good. The solidification temperature range of the zinc-containing high zinc alloy expands, lowers the fluidity, and when magnesium is added, Will generate magnesium oxide in the liquid surface, also reduces the fluidity.
Under the same degree of superheat, the flowability of high-aluminum zinc alloys is comparable to that of aluminum alloys. Due to the wide solidification temperature, segregation may occur, and the segregation tendency increases with the increase of the solidification temperature range. In the ZA type zinc alloy, ZA27 has the highest Al content, the widest solidification temperature, and the most serious dendrite segregation and regional segregation tendency.
Because the Al-rich phase of Al-rich phase is too small and solidifies first, the result of regional segregation is that the zinc alloy is prone to bottom shrinkage holes, and the shrinkage holes are concentrated at the bottom, especially when cooling is slow.
2 welding performance. Die-casting zinc alloy contains aluminum, which forms a layer of A1203 during welding, which is difficult for operation. The only welding repair method that can be used actually is repair welding. For the nickel-plated surface, Cd-Zn eutectic alloy can be used ((Cd82) .5%, Zn 17.5%, Melting point 265 Persuaded for brazing.
3 cutting performance. Zinc alloy has excellent cutting performance, cutting speed can be several times higher than that of gray cast iron, comparable to free cutting brass, and tool wear is also small.
In addition, zinc alloy castings do not suffer from residual stresses due to cutting.
4 zinc alloy. Causes of aging. PI), Sn. Cd is a harmful impurity in zinc alloys. Their solubility in Zn is extremely low. They are adsorbed on the grain boundary and constitute numerous micro-cells. Accelerating electricity at a suitable temperature and humidity. In the chemical etching process, the grain boundaries are bonded loosely and the strength and hardness are reduced, so the content of these impurity elements must be strictly controlled.In addition, the /3 and a phases in the zinc die casting are all in the state of supersaturation, and during use, successively Desolvation, together with the volume of corrosion products on the grain boundary, is also larger than that of the matrix metal, so that the mechanical properties are significantly reduced and the castings grow in size, causing aging.
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