Zn And Pre-deformation On The Extrusion Of Mg-10gd-4.8y-0.6zr Alloy And Room Temperature Mechanical Properties

In this paper, Mg-10Gd-4.8Y-0.6Zr (wt.%) alloy is the based alloy. Zn element was added, and pre-deformation was taken place before aging to this based alloy in order to improve its mechanical properties. Effects of Zn addition and the pre-deformation treatment before aging to Mg-10Gd-4.8Y-0.6Zr alloy were investigated by using digital micro-hardness testing, mechanical testing, optical microscopy(OM), scanning electron microscopy(SEM), X-ray diffraction(XRD) and transimission electron microscopy(TEM). Experiment results are obtained as follows.1) Zn addition can refine the average grains of the as-extruded Mg-10Gd-4.8Y-0.6Zr alloy, with the increase of Zn content the grains became finer. Zn content alloys with the formation of LPS structure had better mechanical properties. The tensile strength and yield strength of the as-extruded alloy with 1wt.% Zn addition, were 37MPa and 43MPa higher than that of the Zn-free alloy, reached 345MPa and 260MPa, respectively, as well as ductility rate reached 13.8%.2) Zn element addition can postpone the T5 peak-aging time of the Mg-10Gd-4.8Y-0.6Zr alloy. The peak-aging time was delayed by the increasing of Zn element, and the values of peak-aging hardness reduced at the same time. The values of tensile strength and yield strength of peak-aging alloy containing 1wt.% Zn aged in 200℃, were 429MPa and 360MPa, respectively,7% and 8% higher than that of the Zn-free alloy, the elongation was 6.3%; In 225℃peak-aging condition, the values of tensile strength and yield strength were 397MPa and 334MPa, respectively, the elongation was 7.0%. When adding too much Zn(more than 1wt.%), the strength of the alloys was significantly decreased, and the elongation of the Zn content alloys increased at first and then decreased with the increasing of Zn content. Therefore, adding 1wt.% of Zn in the Mg-10Gd-4.8Y-0.6Zr alloy can obtain better mechanical properties.3) After cold pre-deformation treatment on Mg-10Gd-4.8Y-0.6Zr as-extruded alloy, the strength of pre-deformation alloys had been significantly improved, for the large number of dislocations and twins formed during the cold pre-deformation treatment, and the values of the strength increased with increase of the degree of deformation, but ductility rate of the alloy reduced in turn. The tensile strength and yield strength of the 15% pre-deformation alloy were 331.8MPa and 290.5MPa, respectively,16% and 64% higher than that of the un-deformed alloy, while the elongation rate fell to 4.1%.4) At the beginning of aging at 220℃, the hardness increased rapidly with the aging time until a peak value of hardness reached at the maximum. There was a plateau of peak-aging region, the hardness of alloys kept a high level at this plateau and then further aging led to a slow decrease in the hardness after 84h. Pre-deformation accelerated the process of aging hardening, when the pre-deformation degree reached 7% or more, the peak-aging time was shortened to 8h. The value of hardness of alloy with 11% pre-deformation was 125HV, which was the highest hardness among all the alloys.5) The tensile strength and yield strength of all the alloys were significantly improved after aging treatment, but the elongation rate of the alloys decreased greatly. When the pre-deformation was 11%, the alloy gained the best mechanical properties, the tensile strength and yield strength were 409.9MPa and 351.5MPa, respectively, elongation rate dropped to 3.9%. Taking both plasticity and strength into account, we can come to a conclusion that it was appropriate when the pre-deformation degree was 11%.