Study On Microstructure And Properties Of Vacuum Die Casting AE44-2 Magnesium Alloy

AE44-2 magnesium alloy is taken as the selected materials,in which the cheap light rare earth elements La and Ce are used as alloy elements.In order to meet the requirements of die casting parts,the effects of vacuum degrees,pouring temperatures and injection speeds on the microstructure and mechanical properties of AE44-2 were investigated and then the die casting parameters were optimized;In order to investigate properties of the alloy at the elevated temperatures,the mechanical properties at the elevated temperatures of the vacuum die casting AE44-2 were studied;To understand the state of the art deeply,the strengthening mechanism at the elevated temperatures,microstructure evolution and microstructure characteristics of the alloy were clarified.It is found that the mechanical properties of the AE44-2 magnesium alloy fabricated via vacuum die casting at room temperature are the optimized when pouring temperature and injection speed are 680 ?and 6 m/s.The yield strength,tensile strength and elongation of the AE44-2 alloy can reach 152.1 MPa,259.6 MPa and19.6 %,respectively.The porosity of the alloy is only 0.195 %.It is found that rare elements in acicular Al11RE3 phase are a mixture of La and Ce.With the increasing of compression temperatures,the work hardening becomes weaker and the dynamic softening becomes stronger.When the compression temperature is at of 200 ?,the geometrically necessary dislocations(GNDs)density reach the highest value of 2.31×1016 m-2?During the whole compression process,the deformation mechanism of the alloy is dominated by dislocation slipping.The dislocation slipping was hindered by Al11RE3 precipitated phase effectively and thus work hardening phenomenon was appeared,which improves strength of the alloy at the elevated temperatures.During the tensile process at the elevated temperatures,with the increasing of the tensile temperatures,the deformation mechanisms shift from work hardening to softening and the fractures of the alloy shift from fragility to toughness.The frequencies of the {10-12} tensile twins increase with the distances from the fracture and the deformation mechanism is still dominated by dislocation slipping.The deformation mechanisms were dominated from dislocation slipping to dynamic recrystallization at 250 ?.