Control of defects in powder injection molded aluminum matrix composites

Machine parameters and flow properties of molding materials play a significant role in controlling the quality of powder injection molded (PIM) parts. Defects in molded parts can cause rejection at the binder removal and sintering stages. In this study, aluminum matrix composites were fabricated by PIM and the origins of defects analyzed. Conventional and multiple live-feed molding (MLFM) devices were used to produce the composites and the effects of machine parameters and flow characteristics of composite mixes on the occurrence of molding defects were studied utilizing X-ray radiography and scanning electron microscopy. Microdefects present were weld lines, microvoids, internal shrinkage cracks, and ejector pin marks. The orientation of fibers was examined in samples with and without weld lines. Specimens prepared by MLFM, were defect free and exhibited highly oriented fibers at the weld line. Macrodefects such as blisters were present on the surface of test samples molded at a higher temperature. From this study, a successful PIM technique has been identified for the production of defect-free 20 mm-thick bars of aluminum matrix composites.