Investigation of Microstructure of Magnesium AZ91HP Alloy for Semi-Solid Forming

Abstract

Semi-solid metal forming is a process for producing high integrity metallic components for various industries. Electromagnetic stirring (EMS) is a typical process for fabricating raw materials used for semi-solid forming. EMS has mainly been used for aluminium alloy, but it is not as developed for magnesium materials. A laboratory-scaled semi-automated electromagnetic stirring apparatus to fabricate magnesium alloys for semi-solid forming was developed. An AZ91 magnesium alloy was selected in this investigation. An optimum process parameter was found to have an electrical frequency of 15 Hz and a melt temperature of 610 °C. The microstructures obtained were equiaxed dendritic grains. The EMS samples were heated and the microstructure was changed to discrete, rosette, oval or spherical shaped particles. Under an optimum heating condition, the microstrucrure resulted in a homogeneous spherical fine grain structure. The average grain size was about 100μm. This indicated that the AZ91HP alloy prepared by this apparatus was suitable for semi-solid forming.