Forming of aluminium alloy at temperatures just below melting point

In order to improve the mechanical properties of products, a forming process of a solid material at a temperature just below the melting point is proposed. The material is deformed at the semi-solid temperature due to the heat generation caused by plastic deformation. The tensile strength, elongation, hardness and toughness of the aluminium alloy (Al-7%Si-0.3%Mg) billet extruded at temperatures between 500 and 550 degreesC are compared with those of the billet extruded in the hot forming (450 degreesC) and the semisolid (560 degreesC) temperatures. The billet temperature during forming is evaluated by the finite element simulation. The tensile strength and hardness of the billet extruded at 550 degreesC just below the solidus temperature are higher than those for a billet at 450 degreesC, and they are almost the same as those for a billet deformed at 560 degreesC in the semi-solid region. The elongation and toughness of the extruded billet at 550 degreesC are lower than those for a billet at 450 degreesC. The forming load at 550 degreesC is almost half of that at 450 degreesC. Cracking on the surface of the extruded billet occurs at a high punch speed. The calculated temperature when the solid billet is extruded in the semi-solid state agrees well with the experimental one at which the tensile and hardness are improved. (C) 2002 Elsevier Science Ltd. All rights reserved.