Semi-solid Magnesium Alloy Composition Evolution And Rheological Properties Of Analysis

Microstructure and composition evolution of MB15 magnesium alloy during semi-solid isothermal heat treatment were researched in this paper. The results showed that compared with AZ91D, MB15 had its characteristic. MB15 could shaping small (Zr play a role on grain refinement, diameter of grain was about 25 μm 50 μm), better spheroidized structure ( worse than AZ91D, for MB15 including elements of Mg, Zn, Zr with hep, grain growing had certain orientation ) with slow grain growing (there were stable compounds including Mg₇Zn₃ and MgZn, which hinder growing of grains).Structure evolution, deformation mechanism and rheologicalteharacteristic of MB15 magnesium alloy, AZ91D magnesium alloy and Zr modified AZ91D magnesium alloy in high solid fraction during compression using two parallel plates were also researched in this paper. Plastic deformation of solid particles played a leading role on the center of specimens, while mixing flow of solid and liquid took a leading position in surrounding place. The adhesion force between solid and liquid was weak tb make the specimen's plasticity bad.Gleeble—1500D simulator was used to carry out the compressive experiments for semi-solid MB15 alloy, AZ91D alloy and Zr modified AZ91D alloy in high solid fraction. The true stress-strain curves were measured directly and then the variations of apparent viscosity with different parameters would be described by using some formula. With increasing the temperature and holding time, the peak stress and steady state stress of three kind magnesium alloys were decreased. When the strain rate ranged from10^-3S^-1 10^-1S^-1, the peak stress increased with increasing the strain rate,and steady state stress decreased. Both MB15 magnesium alloy and AZ91D magnesium alloy in semi-solid had low peak stress and steady state stress.Influenced parameters of rheological characteristic of semi-solid alloys includes temperature, strain rate and holding time. Both MB15 magnesium alloy and AZ91D magnesium alloy in semi-solid were pseudo-plastic, their apparent viscosity decreased with increasing the shear rate. When the shear rate exceeded 5x10^-3s^-1 the apparent viscosity decreased slowly. Another, the apparent viscosity decreased with increasing the temperature. Differences of plots between MB15 magnesium alloy and AZ91D magnesium alloy were obvious, and the regions that the apparent viscosity changed slowly were different because of shape of grains and the spheroidized velocity. Last, the apparent viscosity decreased with increasing the holding time, and the plot variated linearly. When the holding time was less than 2 min, the apparent viscosity of MB15 magnesium alloy was higher than which of Zr modified AZ91D magnesium alloy. When the holding time was more than 2 min, the result was opposite.