Study On Squeeze Processing Of ZA Alloy Casting With High Ratio Of Height To Thickness

Proper parameters were obtained by carrying out the experiments through debugging different parameters. The influence of microstructure, mechanical properties, critical specific pressure and pressure distribution on bar-shaped ZA27 alloy squeeze casting was investigated. The influence significance of parameters to different mechanical properties may be obtained by orthogonal test and other optimized methods .The proper parameters of squeeze casting for bar-shaped ZA27 alloy are: specific pressure 750MPa, mould temperature 170℃-200℃, pouring temperature 600℃-630℃, pressure holding time 45s. Under these parameters, the mechanical properties can reach the level of tensile strengthσ_b≥420MPa, elongationδ₅≥12%, and hardness HBS≥130.The influence of heat treatment on microstructure and properties of ZA27 alloy was discussed. Proper heat treatment processes make the microstructure of ZA27 alloy more homogeneous through 320℃×8h water quenching and 180℃×6h heat treatment, therefore, good mechanical properties are obtained.Relationships of mechanical properties,microstructures,critical specific pressures and pressure distribution were investigated. Squeeze casting, can not only alleviate gravity segregation, uniform the chemical constitution of the casting but also greatly improve the microsegregation of bar-shaped ZA27 alloy. The solidification characteristics of the ZA27 alloys under high pressures were investigated. The effect of cooling process on grain size of ZA27 alloy was also studied.The influence of squeeze casting parameters on strength, elongation, hardness and friction attrition properties of bar-shaped ZA27 alloy was studied. The underlying reasons of different properties at different positions were analyzed, and the way of enhancing uniformity of mechanical properties was discussed. The squeeze casting decreases the differences in mechanical properties of ZA27 alloy, reduces the macrosegregation, enhances the mechanical properties. The distribution rule of pressure and the pressure gradient of axial symmetry cast were thoroughly analyzed, and the mathematical expression of effective pressure and critical specific pressure is established.Friction and wear properties of squeeze casting ZA27 alloy was studied in the paper. With increase in load and at the low sliding speed, friction coefficient of squeeze casting alloy is reduced, wear capacity of squeeze casting ZA27 alloy is excellent. The influence of heat treatment on friction and wear properties of ZA27 alloy was discussed. It shows that the friction and wear properties of ZA27 alloy can be improved significantly by proper heat treatment technique.