The effects of T5 and T6 heat treatments on the microstructure and mechanical properties of extruded Mg–6Zn–1M n alloy were investigated in the present study. The results showed that T5 and T6 treatments could markedly improve the strengths of extruded ZM61 alloy, and the precipitate strengthening effect of double aging was better than that of single aging. The precipitates formed in the T6 treatment were much finer and more dispersive than the ones in the T5 treatment, resulting in stronger precipitation strengthening effect. However, due to additional grain size refinement strengthening effect, the T5 treatment could improve ductility without sacrificing strength over the T6 treatment. Scanning electron microscopy observation and tensile test indicated that different cooling methods after extrusion, such as air cooling and water quenching, had no obvious influence on the microstructure and strengths of extruded and subsequent heat treated Mg–6Zn–1Mn alloys. In addition, the Mn element mainly existed as fine Mn phase particles, which were well dispersed in the matrix. Dispersed Mn particles could be found in rod-like [Formula: see text] precipitates, but not in the disc shaped [Formula: see text] precipitates.

The influence of two-step homogenization on microstructures and properties of AZ40M magnesium alloy were investigated by the scanning electronic microscopy (SEM), X-ray diffraction analysis (XRD) and tensile experiment. Through comparing the microstructure and mechanical properties of the alloy before and after homogenization treatment, a two-step homogenization process of the semi-continuous casting AZ40M magnesium alloy ingot was determined. The result shows that the as-cast AZ40M alloy mainly contained two kinds of second phase, β-Mg17Al12 and Al8Mn5. Treating at temperature of 380 °C for 8 h as the first step homogenization treatment and then treating at temperature of 420 °C for 20 h as the second step homogenization treatment made the eutectic phase (α-Mg/β-Mg17Al12) completely eliminated and the alloying elements such as Al, Zn distributed uniformly. Al8Mn5 is the residual second phase in the homogenized AZ40M alloy. During the homogenization process, the β-phase dissolved which made the content of Al increased in the matrix. The decomposition of β-phase benefits the tensile strength and elongation of the alloy. The tensile fractures of as-cast and homogenization alloys are characteristic of ductile fracture.

The hot deformation behavior of Mg-12Gd-1MM-0.6Zr (wt.%) magnesium alloy was tested by Gleeble-1500D hot simulator with reduction of 60% and strain rates from 0.001 to 1 s−1 at the temperature range from 753 to 793 K. The results show that the flow stress is influenced by both, temperatures and strain rates. At constant temperatures, flow stress is increased with strain rate, while at constant strain rates, it decreased with temperature. The constitutive equation of Mg-12Gd-1MM-0.6Zr alloy during hot compression was constructed by the linear regression analysis. Average activation energy and stress exponent were 227.94 kJ/mol and 2.87, respectively. The processing map was plotted and analyzed via the dynamic material model. The most proper ranges for hot deformation temperature and strain rate were found to be 763 to 783 K and 0.01 to 0.1 s−1, respectively.

Cooling curves and residual deflection during spray quench process are measured by using thermometric instrument and spiral micrometer, separately, in extruded EW75 magnesium alloy. By using Numerical analysis, temperature and stress with the change of time during quenching were also investigated. The results showed that: when the spray speed was 6L/min, the steam film stage was obvious, as the speed reached to 9L/min, steam stage disappeared. The residual deflection increased with the spray speed increased. When the spray speed was 6L/min, the residual deflection was 3.38mm and increased to 3.88mm as the spray speed increased to 9L/min. But with the increase of spray speed, the growth rate of deflection induced. The results of the numerical simulation indicated that during the quench process, the surface cools faster than body and shrink more severely at first, leading stress distribution is compress at surface while tensile in body. Plastic deformation happens at this time. And then along with the surface cooling speed reduced, the body cool speed is greater than surface; the shrink in body is also greater, thus the compress stress turn to be tensile and contrary change take place at surface. With the increasing distance from the cross section, the tensile stress is reduced gradually, in 5.3mm, there exists a zero stress layer, then turns to compressive stress.