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Tapered handlebars using high strength aluminum alloys have been applied mainly to motorcycle models requiring weight reduction and high texture appearance that aluminum handlebars can offer as their characteristics. This handle bar is manufactured through extrusion processing. Conventionally used alloys had low extrusion productivity, which led to increased cost of the handlebars. In view of this, we selected an alloy securing the strength by adding a large amount of zinc while reducing the amount of the copper, which deteriorates the extrusion productivity, to the minimum adding amount, in consideration of maintaining the stress corrosion cracking resistance. However, a large amount of zinc decreases the stress corrosion cracking resistance. Therefore, in order to obtain a metallic structure favorable to the prevention of stress corrosion cracking, the mandrel extrusion was applied for the pipe manufacturing method, and heat treatment condition and swaging condition were optimized.

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.