Effects of reinforcement particle size in MMCs on extrusion die wear

In this study, extrusion die wear during the metal matrix composite (MMC) extrusion process was investigated with regard to the size of the reinforcement particle. Extrusion die materials were AISI H13 hot working die steel and were machined by EDM in order to gain rectangular and circular die bearings. The dies were hardened, tempered and grounded to be prepared for extrusion processes.AA 6063 aluminium matrix composite billets reinforced with SiC particles (Al/SiCp) were prepared by stir casting method for extrusion process. Different SiC particulate sizes (53 μm, 167 μm and 478 μm) and constant volume fraction (10%) were used for the reinforcement of the matrix. Extrusion processes of the prepared composite billets were conducted at 500 °C with ram speed of 2 mm/s and extrusion ratio of 25:1 under laboratory condition.The variation of die wears with SiC particle size was characterised by weight loss in the die as a result of extrudate length and roughness of the die bearing surface. SEM and OM studies were also carried out for the observation of wear mechanism of the die bearing surfaces.The results of this study show that the die wear is affected differently by the SiC particle size. The SiC size of 167 μm is a critical size for die wear during the Al matrix composite extrusion process, since the die wear and surface roughness increase up to the size of 167 μm and then they decrease although the SiC particle size in the billets increase up to 478 μm. The wear mechanisms of the die bearing surface are predominantly abrasion with microcutting, wedge-forming and ploughing modes.