The Effect Of Two-stage Aging On Microstructure And Properties Of ZM6Magnesium Alloy

In this paper, electronic optical microscopy, X-ray diffraction, scanningelectron microscopy, transmission electron microscopy, Brinell hardness anduniversal tensile tester are used to study the microstructure, mechanicalproperties and its variation of magnesium alloy under different ZM6agingprocess conditions. Obtain the following conclusions and analysis:Low temperature pre-aging process take the solution process530℃×14h,the regulation of pre-aging temperature(80~130℃), pre-aging time (0.25~4h),the final aging process200℃×8h for ZM6magnesium alloy heat treated, theresults showed that, with the increasing of pre-aging temperature, thephotomicrograph has no significant difference in average grain size rangebetween39.25~41μm, low pre-aging temperature had little effect on the grainsize, With the extension of pre-aging time, the alloy hardness, strength graduallyincreased and then leveled off at first, continue to delay alloys little change.Alloy fracture is given priority to cleavage fracture, most of are the intergranularfracture, part along the crystal transgranular mixed. Macroscopic fracture is flushand the granular with darker colour. Optimal aging process parameters:530℃×14h+100℃×4h+200℃×8h, TEM observation of the sample after pre-aging appear GP zones totally coherent with the matrix, and after the secondaryaging these GP area as heterogeneous core grow small dispersion of precipitatedphase. The overall of the alloy strength hardness increased first and thendecreased, the yield strength153MPa, tensile strength263MPa, Brinellhardness81.3, compared with the single-stage aging process, two-stage agingprocess greatly improves the mechanical properties of the alloy.High temperature pre-aging process take solid-solution process530℃×14h,the regulation of pre-aging temperature (240~360℃), high pre-aging time (2.5~12.5min), the final aging process200℃×8h for ZM6magnesium alloyheat treated, the results show, with the pre-aging temperature increased, theaverage grain size in the range between39.64~43.88μm, short-term high-temperature pre-aging temperature had little effect on the grain size. The overallstrength and hardness of the alloy increased first and then decreased. With theextension of pre-aging time, the strength and hardness of the alloy graduallyincreased to maximum then rapid decline. Fracture cleavage fracture is still themain mode, there appear torn edges.At530℃×14h+280℃×10min+200℃×8h, alloy has optimal mechanicalproperties. After pre-aging precipitation phase has coherent relation with thematrix, after the secondary aging phase grows up, with the semi-coherent tomatrix. The yield strength168MPa, tensile strength of268MPa, Brinellhardness82.9, compared with the single-stage aging process, two-stage agingprocess not only improves the mechanical properties, but also greatly reduces thetreatment time.