A Fundamental Study On Net-shape Hot-pressing Of Mg Cast Perform

Introducing plastic deformation during net-shape forging of preformed Mg casting produced by gravity or squeeze casting sounds to be an economic process to produce high performance Mg parts. To technically take the advantages of the press deformation of cast perform and to lay a sound base for the development of low-cost"net-shape forming of high performance Mg structure by hot-press of Mg cast perform"technique, the press deformation behavior of Mg casting was empirically evaluated and the relationship between processing temperature, pressing speed, pressing stress and deformation rate was modeled. The evolution of the casting microstructure and changes of their mechanical properties subjected to press deformation and post heat treatment were characterized. The effects of press deformation on the morphologies of cast imperfections were observed in the present study. The main achievements of the present studies are summarized as follows.1. By systematical experimental pressing of AM60B cast columns, the relationship between processing temperature(573～673K), pressing speed, pressing stress and deformation rate were investigated. A statistic model of the relationship was established by multivariate regression analysis of the experimental data. Here,σ-- the flow stress (MPa)ε-- the logarithmic strain T -- the deformation temperature (K)υ-- the compression speed (mm/min)2. To predict the evolution of cast microstructure and property and to guide the design of cast perform geometry and the regulation of the following up deformation distribution, numerical simulation of the pressing of AM60B was carried out and the distribution maps of the internal stress and strain within the forged casting were visualized. The influence of main processing parameters, such as temperature, pressing speed, pressing force and deformation rate on the internal stress and strain distributions were investigated. The microstructure evaluation and recrystalization behavior were empirically characterized in comparison with numerical results.3. The microstructure of AM60B Mg alloy in both as-cast and pressed conditions was characterized by light microscopy. The plastic deformation behavior ofα-Mg and second phases in different deformation zones was investigated. The influence of temperature, pressing speed, compression ratio, and post treatment on the morphology evolution, recrystalization ofα-Mg matrix, and the morphological changes and re-distribution behavior of the second phases were investigated. The aboves, in turn, provide reference guidance to the geometry design of cast perform and the control of plastic deformation distribution within the forged Mg part and the related properties design.4. The effects of press deformation on the morphologies of cast imperfections were observed. The morphology evolution and the influence of main processing parameters in press deformation were investigated. The mechanism of cast imperfections closing and repairing was proposed, and the closing and repairing mechanics of press deformation on cast imperfections was developed.5. The mechanical properties of AM60B alloy subjected to hot-pressing and heat treatment were investigated by tensile test, and the influence of plastic deformation temperature, pressing speed, compression ratio, and post heat treatment on the properties were investigated to provide guideline to the design of Mg forging parts.A patented technique named as"The net-shape forging of Mg cast perform"was developed, which, in turn, lays a sound base for the low-cost production of high performance Mg parts.