Back Pressure Extrusion of Brittle Metals and Metallic Powder

概要

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Experimental studies were made on the effects of back pressure in the extrusion process of some brittle metals, in connection with their fracture characteristics under high pressure. Extrusion apparatus with solid back pressure was newly developed for this purpose. The results show that : (1) the fracture strain in compression test increases almost linearly with the surrounding pressure ; (2) a certain critical back pressure is present to prevent cracking in the extruded products of the brittle metals ; (3) the V-type crack is produced in the core of the magnesium billet, while in Al-Cu-Si alloy the fir-tree type crack also appears on the surface ; (4) the extrusion temperature as well as the back pressure has effect on the cracking of Mg-Al alloy ; (5) the prevention of cracking in tube extrusion is more difficult than in rod extrusion ; (6) the critical back pressure in high speed extrusion of Al-Cu-Si alloy is much lower than that in low speed extrusion ; and (7) the sintered copper powder is extruded without cracking at high speed by the application of appropriate back pressure.
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