锌压铸合金

[中文适用范围]： 由于压铸过程中涉及剧烈的激冷，以及铝和铜在锌中的固溶度随温度变化的事实，这些合金会发生一些时效变化，其中之一是尺寸变化。两种合金在铸造后都会经历轻微的收缩，在室温下，五周内大约完成三分之二。可以通过稳定退火来加速这种收缩，之后不会发生进一步的变化。建议的稳定退火为 100℃(212℃@) 3 至 6 小时，或 85℃(185℃@) 5 至 10 小时，或 70℃(158℃@) 10 至 20 小时。情况是从铸件达到退火温度时开始测量的。退火后，零件可以空冷。这样的处理会导致大约三分之二的收缩率（每英寸0.0004英寸）和剩余的收缩率。将会在接下来的几周内在室温下发生。稳定化会导致尺寸比铸件的原始尺寸减少约 0.0005 英寸。如果机器或装配操作可以延迟到铸件在室温下已老化五周。当暴露于停滞的湿气或与氧气接触有限的凝结@时，锌压铸件@可能会发生不均匀类型的腐蚀@，这通常会导致形成大量白色腐蚀产物薄膜。这可能会阻碍汽车锁芯@燃油泵@和化油器@等部件的运行，严重时会导致锌的快速流失。各种类型的铬酸盐薄膜可以很好地克服这种情况。两种合金均采用相同的电镀或搪瓷程序。有机饰面与锌表面的良好粘附能力差异很大。磷酸盐类型的化学预处理已获得最广泛的商业应用，大多数要涂漆或搪瓷的锌压铸件都经过磷酸盐预处理。一般来说，经过预处理的压铸件可以使用更广泛的饰面选择。两种 SAE 合金的相对优点可概述如下： [外文原描述]： Because of the drastic chilling involved in die casting and the fact that the solid solubilities of both aluminum and copper in zinc change with temperature, these alloys are subject to some aging changes, one of which is a dimensional change. Both of the alloys undergo a slight shrinkage after casting, which at room temperature is about two-thirds complete in five weeks. It is possible to accelerate this shrinkage by a stabilizing anneal, after which no further changes occur. The recommended stabilizing anneal is 3 to 6 h at 100 °C (212 °F), or 5 to 10 h at 85 °C (185 °F), or 10 to 20 h at 70 °C (158 °F). The time in each case is measured from the time at which the castings reach the annealing temperature. The parts may be air cooled after annealing. Such a treatment will cause a shrinkage (0.0004 in per in) of about two-thirds of the total, and the remaining shrinkage will occur at room temperature during the subsequent few weeks. Stabilizing results in a decrease in dimensions of about 0.0005 in per in from the original size of the casting. Stabilizing is, of course, unnecessary if the machine or fitting operations can be delayed until the castings have aged five weeks at room temperature.When exposed to stagnant moisture or condensation with limited access to oxygen, a nonuniform type of corrosion may occur on zinc die castings, which often results in the formation of a bulky film of white corrosion products. This may hinder the operation of such parts as automobile lock cylinders, fuel pumps, and carburetors, and in severe cases result in rather rapid loss of zinc. Various types of chromate films are available to satisfactorily overcome this condition.The same electroplating or enameling procedure is used with both alloys. Organic finishes are quite variable in their ability to adhere well to zinc surfaces. The phosphate type of chemical pretreatment has received widest commercial utilization, and most zinc die castings which are to be finished with lacquers or enamels are phosphate pretreated. In general, a much wider selection of finishes can be used on pretreated die castings.The relative merits of the two SAE alloys may be outlined as follows:Cross Reference: