The Research On The Fundamental Problem Of ZA27 Alloy Squeeze Casting With High Ratio Of Height To Thickness

The fundamental problems of ZA27 alloy squeeze casting with high ratio of height to thickness were studied in this paper. Proper parameters were obtained by designing the plunge squeeze casting die and carrying on the experiment through debugging different parameters. The influence of squeeze casting on mechanical properties and microstmcture of ZA27 alloy was also investigated.The influence significance of parameters to different mechanicals may be obtained by orthogonal test .The proper parameters of squeeze casting for ZA27 alloy with high ratio of height to thickness are: specific pressure 750MPa, mould temperature 170℃²00℃, pouring temperature 600℃⁶30℃, pressure holding time 45s. Squeeze casting can ameliorate the mechanical properties discrepance of different parts of the same casting and improve the mechanical properties of the casting. Under proper parameters, the mechanical properties index can attain the level: tensile strength σ≥420MPa, elogation δ₅≥12%, hardness HBS≥130.Squeeze casting can apparently ameliorate the macrostructure of ZA27 alloy. Under pressure the macrostructure is compacted without serious deficiency such as shrinkage cavity, shrinkage porosity, pore and so on. Squeeze casting can also apparently ameliorate the microstructure of ZA27 alloy with high ratio of height to thickness. The microstmcture changes to flowerlike dendritic from treelike crystal after squeezing. Squeeze casting also changes the shape of intercrystal eutectics. The eutectics appear big strip shape under normal atmosphere, well under pressure appears small layered shape. Under pressure the structure of different parts of the same cast still appears some discrepance. The microstmcture of the upper part and lower part is finer than that of the middle part .The microstmcture of outboard is finer than that of the inside. The microstmcture of center part is fine equiax crystal. The microstmcture of outboard is close grain with the feature of deforming structure.Squeeze casting can not only ameliorate gravity segregation uniforming the chemical constitution of the cast but also the microsegregation of ZA27 alloy with high ratio of height tothickness. Squeeze casting can decrease the segregation proportion of Zn, Al, Cu, and increase the Al content of intercrystal eutectic and the Cu, Zn content of a dendritic. Squeeze casting also bring change to the solidifying process of ZA27 alloy. Differential thermal analysis shows that at the temperature of eutectic reaction, an endothermic peak vanishes under the pressure of 750MPa. It also shows that pressure restrains the occurrence of eutectic reaction.