Creep deformation study of squeeze cast AZ91 magnesium alloy

Abstract

The AZ91 magnesium alloy has excellent mechanical properties; however, its application is limited by its poor creep resistance. In this study, AZ91 magnesium alloy prepared by squeeze casting technique has been tested for its creep performance at varying stresses and temperatures. The governing creep mechanism was examined in the wake of deformation. The microstructure for as-cast AZ91 alloy confirmed the massive dendritic β-Mg17Al12 phase. The creep study indicated that the governing creep mechanisms were dislocation creep and dislocation climb governed by lattice diffusion in the test regime of 50 MPa stress at 150oC to 175oC. The measured dislocation density values showed good agreement with the expected dislocation density in the power law creep mechanism.

Effect of Individual Alloying Addition on the Microstructure and Creep Behavior of Squeeze Cast AZ91 Magnesium Alloy

“…The flat creep testing sample was prepared according to the ASTM E-139 testing standard and allowed to undergo constant load tensile creep test at 50 MPa of stress and 175 o C temperature. For detail on the creep testing machine and procedure, kindly see articles [3,4]. The vicker microhardness test was performed on the investigated alloys with the 300 g force and 20 s dwell time.…”

“…Magnesium is the lightest structural material available, with a density of 1.8 g/cm 3 , which is 33% of aluminum and 75% of steel [1,2,3]. Employing lightweight magnesium and its alloys in automobile industries enhanced automobile fuel efficiency by reducing the vehicle's overall weight and reducing CO2 emission [4,5]. Magnesium automotive applications include cylinder blocks, steering wheels, gearbox and housing, transmission cases, etc.…”

“…Magnesium automotive applications include cylinder blocks, steering wheels, gearbox and housing, transmission cases, etc. The application of squeeze casting (SC) over die casting (DC) delivers better casting with a high-quality surface and less porosity [4,6].…”

“…The inclusion of these elements causes the precipitation of thermally stable intermetallic or Mg matrix strengthening via solid solution. These intermetallics are capable of obstructing the grain boundary migration and dislocation motion during high temperatures deformation [4,7].…”

“…Hot cracking and solidification cracks appeared during die-casting. Employing a squeeze casting (SC) can overcome these challenges associated with castability [4]. Cerium (Ce), more expensive than Ca and the most abundant rare earth metal, provides necessary fluidity during casting.…”