Development of Aluminum Powder Metal Composite Material Suitable for Extrusion Process used for Cylinder Sleeves of Internal Combustion Engines

There are a couple of ways to manufacture aluminum cylinder blocks that have a good balance between productivity and abrasion resistance. One of them is the insert-molding of a sleeve made of PMC (Powder Metal Composite) by the HPDC (High Pressure Die Casting) method. However, in this method, cracks are apt to occur on the surface when the PMC sleeve is extruded and that has been a restriction factor against higher extrusion speed. The authors attempted to raise this extrusion temperature by eliminating the Cu additive process from the aluminum alloy powder in order to raise its melting point by approximately 50 °C. This enabled the wall of the extruded sleeve to be thinner and the extrusion speed to be higher compared to those of a conventional production method while avoiding the occurrence of surface cracks. Moreover, it was found that the dispersion of Fe-Si compounds into fine particles by adding a large amount of Fe is effective as a way to maintain the necessary hardness without adding Cu. Furthermore, we clarified the effect on the ratio of surface area composed of the crystalized materials created by the addition of Fe and Si. Thus, we found a new way to improve seizure resistance by controlling the area ratio of hard particles. Based on these findings, we successfully developed a PMC sleeve alloy that had the equivalent or higher seizure resistance compared to the current alloy and allowed the high-speed extrusion of thin-wall sleeves.