Investigation into machining performance of microstructurally engineered in-situ particle reinforced magnesium matrix composite

Abstract

Magnesium and magnesium in-situ composites have significant potential in the application of design and manufacturing for automotive and aerospace industries because of their high specific strength and reduced fuel consumption. But there are many challenges for machining of Mg based alloys and composites because of the high tendency of fire and oxidation. These challenges can be minimized through microstructural engineering. In this present study, the machining performances of AZ91 Mg alloy and in-situ hybrid TiC+TiB2 reinforced AZ91 metal matrix composite was investigated. The effect β-Mg17Al12 phases and grain refinement with and without in-situ particles on machinability were studied through microstructural engineering via aging and friction stir processing. The end milling operation was carried out at different cutting speeds ranging from 25 mm/min to 90 mm/min under dry environment by using an AlTiN-coated tungsten carbide tool. The optimum cutting speed for machining was found to be 75 mm/min based on the surface roughness values of all conditioned materials. The base material with dendritic microstructure was found to have poor machinability in terms of inadequate surface finish and edge-burrs formation. The combined effect of in-situ TiC+TiB2 particles addition and grain refinement enhanced the machining performance of the material with superior surface finish, negligible edge-burr formation and better tool wear resistance. The influence of in-situ TiC+TiB2 particles, β-Mg17Al12 phases and grain refinement on machining characteristics are explained based on the tool wear mechanisms, chip behavior and machining induced affected zone.

Keywords

• Magnesium
• In-situ composite
• End-milling
• Tool wear
• Chip morphology