Research On Elevated Temperature Deformation Performance And Mechanism Of Mg-xAl(x=3,6,9Wt.%)

In this topic, pure Mg (99.98%) and pure Al (99.97%) were melted and cast toget the ingots of Mg-xAl (x=3,6,9wt.%), adopted the homogenizing annealing of420℃×8h to eliminate the segregation of the ingot, then, rolled the ingot with theTwo-high (roughing rolling) and Six-high (finish rolling) rolling and got the Mg-xAl alloysheets with3mm, finally, the stress relief annealing were carry out at300℃for2h.High temperature tensile tests mainly included the elongation to the fractureexperiment (EF), the elongation to the fixed strain and strain-rate change (SRC)experiment. The observation and analysis were performed by using the metallographicmicroscope, SEM and TEM. The results are as follows:The microstructure of rolled Mg-xAl alloy sheet are mainly fine grain withfalsification, after the stress relief annealing, the microstructure was almost theequiaxed grain with some twin crystal existing, the grain sizes of Mg-3Al, Mg-6Aland Mg-9Al alloy sheets, respectively, are32,48and59μm. The fracture of Mg-xAlalloy after high temperature tensile is consisted of equiaxed dimples and paraboladimples, the fracture mode is typical ductile rupture. TEM and energy spectrumanalysis showed, the second phase particle is almost non-existent in Mg-3Al alloy, thesecond phase particles are found in Mg-6Al and Mg-9Al, with similar shape oflamellar or rod, the number of the second phase in Mg-9Al alloy were more than thatof Mg-6Al alloy.In the temperature interval of350～450℃, at the strain rate of10-2s-1,dislocation climb creep is the leading mechanism in the deformation process ofMg-3Al, Mg-6Al and Mg-9Al alloy; at the strain rate of10-3s-1, the deformationmechanism of Mg-3Al and Mg-6Al alloy are competition mechanism of solutepinning dislocation creep and dislocation climb creep, and the main deformationmechanism of Mg-9Al is solute pinning dislocation creep, with the decreasing ofstrain rate and the increasing of Al, dominant deformation mechanism of the alloychanged from dislocation climb creep to solute pinning dislocation creep. In thetemperature interval of400～450℃, at the strain rate of10-3s-1, the deformationmechanism of Mg-3Al, Mg-6Al and Mg-9Al are solute pinning dislocation creep.