Microstructure And Mechanical Properties Of Al-25Mg Binary Alloy Solidified Under High Pressure

In this paper, the solidifications of Al-25Mg alloy under high-pressure andrapid quenching condition have been investigated. The selected pressures forhigh-pressure solidification are1GPa,2GPa and3GPa, and the rotation speed ofthe cooling wheel is25m/s and35m/s respectively. The microstructural characterand the phase composition in Al-Mg alloy have been analyzed, and the mechanicalproperties of the alloy under high pressure solidification have been studied.The phase and microstructure of Al-25Mg alloy changes under the highpressure, the intermetallic βphase is no longer exist, and transforms to the γ phaseand Al(Mg) solid solution. When the pressure further increases, the γ phasedisappears and the alloy is constitutes solely by solid solution. During the phasetransition, the morphological character of the alloy changes all along. Comparedwith the microstructure obtained under common pressure, the primary dendrites aremuch more developed under high pressure with reduced secondary arm spacings.The increase in the pressure increases the melting point and viscosity, which makesthe primary dendritic arm less likely to melt during melting.The solid solubility of Al-25Mg alloy varies under high pressure, when thepressure increases, the solid solubility of Mg in alss increases. Meanwhile, the solidsolubility of Mg differs in the alloy, i.e. Mg is heterogeneously distributed in thealloy.The mechanical properties of high-pressure solidified samples show that thetensile properties of Al-25Mg alloy have been greatly improved after high pressuresolidification, tensile strength of alloy solidified under3GPa pressure is4timeshigher of that solidified under1GPa pressure. And the fracture behavior transitsfrom brittle fracture to ductile fracture. The hardness of alloy decreases withincreasing pressure. As the brittle intermetallic phase in the alloy decreases, theductile solid solution phase with good toughness increases, which improves alloymechanical properties.A homogeneous supersaturated solid solution is obtained during rapidsolidification.The microstructure of the rapidly solidified Al-25Mg alloy shows thatnear the Cu wheel side, the alloy is planar growth, while the air side is dendriticgrowth, the reason for such morphological variation is the degree of undercooling isdifferent on the two side. Microstructure under rapid solidification is morehomogeneous. The planar growth areas constitutes a larger part of the total crosssection when the rotation speed is35m/s than is25m/s.