Research On Hydroforming Of AZ31 Magnesium Tube At Differential Temperature Field

With the low plastic at room temperature, it is hard to form complex structural parts by Mg alloy. Hydroforming at elevated temperature can improve the plastic and enhance the forming limit, but with this method, the thickening of feeding zones are serious and the uniformity of thickness of tube is low. This paper do the research on hydroforming of AZ31 Mg alloy at differential temperature field, for reducing the thickening of feeding zones and improve the uniformity of thickness of tube.First of all, this paper does the mechanical properties testing and microstructure analysis of AZ31 Mg alloy tube. Taken the tensile specimen along the tube axis, observing and analyzing the original microstructure of tube and the microstructure with different tensile conditions by testing the temperature range from room temperature to 260℃,strain rate 0.1 s-1,0.01 s-1,0.001 s-1. Analysis shows that with the increasing of temperature, material yield strength and tensile strength was significantly decreased, although the total elongation significantly increased, but the uniform elongation decreases.With the result of tensile properties at different temperatures and strain rate, carried out the hydroforming of AZ31 Mg alloy tube at differential temperature zones. Design the die of hydroforming at differential temperature zones and established the temperature field along tube axis with different temperature discrepancy. Research the influence of the parameter of loading curve,temperature of forming zone,temperature discrepancy,loading rate and so on. With the molding with expansion rate of 30%, the thickening rate of feeding zone is 5%, which is more than half of the normal hydroforming. By the hydroforming at differential temperature zones, the largest expansion rate reached 66.2%.Analyze the microstructure of formed tube, we found that there is difference in temperature during the deformation, which lead to the difference of microstructure along the tube axis. The feeding zone and the transition zone with low temperature exist twins, relatively, the forming zone with high temperature occurred complete recrystallization.