Microstructure Evolution Of Mg-10Gd-3Y Alloy During Thermal Plastic Deformation

With the development of industrial technology, magnesium alloys are widely used as the lightest structure material. However, most of the magnesium alloys only suit to be used at low or moderate temperatures. Consequently, increasing attention and efforts have been paid to research and development of heat resistant magnesium alloys. Previous research work has demonstrated that the mechanical properties of magnesium alloys at room temperature and high temperature could be obviously improved by alloying with rare-earth elements, especially with heavy rare earth gadolinium, yttrium and so on. The present work firstly calculated microstructures and phase compositions of GW103 alloy under the different treatment processes by Panda software. And then, compression test at high-temperature was simulated to investigate deformation behavior and microstructure evolution of this alloy. Finally, forging deformation was carried out according the result of compression test. The effects of different forging conditions on microstructure and mechanical properties were analyzed.The results of phase-diagram calculation showed that:(1)As-cast GW103 alloy is mainly composed with a-Mg matix, Mg5Gd, Mg24Y5 and MgZn at room temperature. The molar fraction of Mg24Y5,Mg5Gd, and MgZn is 0.06,0.1 and 0.01,correspondingly.(2)Through solid solution treatment at 520℃for 24h, phase composition of the alloy consist of a-Mg and non-equilibrium Mg-RE phase.The peak flow stress of as-cast GW103 alloy increased with increasing strain rate and temperature. As for the solution-treated sample, the deformation resistance increased which implied that it is difficult to hot deformation for the solution-treated sample. The best deformation temperature, strain rate and strain were optimized to 450℃,0.1/s'1 and 60% for the solution-treated alloy.The hot-forging experiments were carried out based on the results of hot compression experiment. The results showed that the single direction forging at 450℃exhibited typical thermal processing characteristics. Mechanical properties became larger and grain size became smaller with increasing strain rate, increasing strain and decreasing temperature.While for the multi-direction forging at constant temperature, dynamic recrystallization became much more completed and the microstructures evolved to more uniformity. Much finer and homogenous grains could be gained by multi-direction forging at descending temperature. It is because the new dynamic recrystallization grains were reserved and their growth could be suppressed under this deformation conditions.Φ220×540mm ingot was forged at the multi-directions on the basis of hot-compression simulation. No obvious crack was observed at ingot surface, which suggested that this alloy exhibit good deformation ability. Mechanical properties of the forged alloy were tested. The results showed that the ultimate tensile strength at central region of top, bottom, arc and sides of forging ingot were about 360-385MPa,370-380MPa,345-360MPa and 390-415MPa, separately, and elongation of all sides were about 6.0%-8.0%. Experimental results demonstrated that it was feasible to obtain optimized hot-forging parameters by hot-compression simulation experiment.