Investigation On Structures And Properties Of Die-cast AZ91D Magnesium Alloy

Because of lower density ,high ratio of strength to density and others advantages, Magnesium alloy is an important engineering structure materials used widely to produce 3C (computer, communication and consumption) and automobile products.In the paper ,microstructure evolutions, mechanical properties, small pox phenomenon on the surface, and corrosion mechanism of die-cast magnesium alloy AZ91D,have been investigated and discussed in detail by means of metallography, SEM, tensile strength testing and salt spraying test combined with computer-aided flow in die analysis, some important conclusions are got and listed in the following1 Structure of the die-cast magnesium alloy AZ91D is composed of global-like structure, which is fine and homogeneous, and actinomorphous dendritic grains. On the contrary, a kind of coarser structures and some metallurgical drawbacks, such as micro-holes and shrinkages, will appear in the mould-cast alloy thus mechanical properties of the latter is poorer than that of the former.2 When in different part or the casting thickness not equal, the die-casting magnesium alloy AZ91D has different mechanical property. Usually, the thinner of the casting wall, the better of the mechanical property.3 The reason of the cold flaw is that the temperature in themould is not uniform. In the thrusting examination, it's found that the cold flaw doesn't have obvious bad effect to the casting.4 Essentially, the small pox in the die-casting or the painted-casting is same. As there are impurities in the matrix, the constitution is loose, and the compact density is poor, then a channel will appear to make the matters in the matrix exchange with the outer environment. In normal temperature, the impurities will have chemical reaction, and then the small pox will be seen at the surface.5 Through analyzing the salt sprat testing of the phosphorous casting, it is found that the morphology of the corrosion products of the AZ91D is different, but the reason is same, it's all caused by the impurity in the constitution or the surface looseness. While the wrong phosphorous procession will also make corrosion.The above achievements have partly been used in the practical production, and solve many problems that always affect the quality of the products, at the same time the good economical and social benefit are got.