Research On Technological Basis For Quick Plastic Forming Of ZK60 Magnesium Alloy Sheet

Quick plastic forming technology which requires the strain rate to be less than 10-2s-1 and the forming time to be in few minutes can form panel parts in ten minutes with the aid of rapid heating and cooling technology. This technology doesn't obtain the best superplasticity, but only to make plasticity to meet requirements. The parts which have complicated shape can be formed in one time with this technology. So this technology can be used in mass production. The strength of ZK60 magnesium alloy is the highest in commercial alloys, so it is very important to study the quick plastic forming law of this sheet in order to gain light-weight and high strength magnesium alloy structure parts.This paper use ZK60 magnesium alloy rolled sheet with the thickness of 1.2mm as the study object. In order to obtain the mechanical properties and material parameters related to quick plastic forming, the hot tensile tests are performed. The hot tensile tests are carried out at a temperature range from 250℃to 400℃and strain rate range 10-3s-1~ 10-2s-1 . The biggest elongation is obtained at 350℃. The flow stress decreases as the temperature rises or the strain rate descends. Firstly domes are formed by 5 minutes'quick plastic forming experiments, the height of the forming parts is considered as the standard which choose the proper forming temperature and gas pressure, and then the wall thickness distribution is analyzed. Experimental results show that the biggest bulging height of 37.04mm occurred at 350℃,0.85MPa. The position of the smallest thickness is in the top of the domes. The thickness increases as the distance increases from the top. According to the domes'experiments, the cylinder-shaped and box-shaped parts are made under 350℃.The maximum forming height of cylinder-shaped parts is 22mm and of the box-shaped parts is 20mm. The thinnest position of the cylinder-shaped and box-shaped parts is in the bottom corner.The numerical results which are carried out using commercial finite element software Marc show that the strain rate is up to 10-2s-1 and the thickness distribution is fitted well with the experimental results.The effect of temperature and thinning rate on microstructure evolution is tested by metallographic analysis. The SEM results show that the micro-fractured mechanism of quick plastic forming for ZK60 magnesium sheet is microvoid accumulation fracture.