Study On Microstructure And Properties Of Squeeze Casting ZA27 Alloy

Squeeze casting, the same as Liquid forging, which is a forming process between die casting and forging. Filling and solidification of liquid metal were taking under pressure, which offered forced feeding. The castings are characterized with fine grains, compact structure, no defects of shrinkage and loose, which is comparable with forgings in mechanical properties. The research on the temperature distribution during the process of squeeze casting makes sense in optimizing the process parameters. Otherwise, in order to further improve the mechanical properties of ZA27 alloy, appropriate process parameters of heat treatment is also very important.The numerical simulation of the relationship between initial mold temperature and the temperature distributions of forming process of squeeze casting ZA27 worm was taken. The effects of initial mold temperature on the forming process of ZA27 worm casting were analyzed and discussed by combining the results of numerical simulation by using FEA software Deform with the problems occurred in actual production process. The results show that necessary dwell time increased with the increase of initial mold temperature gradually. The effect of heat preservation of central portion enhance and the solidification point move close to inner side of casting. The appropriate process parameters as followed can enhance the mechanical properties of casting, prolong mold life and raise productivity: pouring temperature: 600oC; specific pressure: 68.96MPa; standing time: 14s; speed: 20mm/s; initial mold temperature: 200 oC.In order to study the effects of different forming process to microstructure, hardness, tensile strength, elongation and wear and friction property of ZA27 alloy, the microstructures and mechanical properties of squeeze casting ZA27 alloy and permanent gravity casting ZA27 alloy were compared. The results show that, compared with permanent gravity casting, squeeze casting ZA27 alloy has fine grains, compact structure and no shrinkage. Gravity segregation and heterogeneous structure is improved. The shape of rich-copper ε phase transforms from discontinuous reticulation structure into micro particles with diffuse distribution. As a result, squeeze casting ZA27 alloy with uniform microstructure has better performance in hardness, tensile strength in ambient and high temperature and wear and friction property.The solution and aging treatment of squeeze casting ZA27 alloy were studied by observing alloy’s microstructure and measuring its hardness and electrical resistivity. It is shown that, solution temperature at 370 oC and heat preservation for 5h, the squeeze casting ZA27 alloy can solute adequately results in obvious enhancement of mechanical properties. After solution treatment at 370 oC, heat preservation for 12 h, ZA27 alloys were aging at the temperature of 50 oC, 70 oC, 100 oC and 150 oC, respectively. With the increase of aging temperature, hardness peak value appeared earlier and decreased gradually. Desolution mechanism transform as follow: discontinuous desolution, discontinuous desolution + spinodal decomposition, spinodal decomposition. During the process of aging treatment, the decrease of solid solubility plays leading role to reduce the electrical resistivity of ZA27 alloy. With the transformation of desolution mechanism, the changes of electrical resistivity at the early stage in the aging process under different aging temperature were volatile.