Abstract:Semi-solid microstructure of industrial hot extrusion rod was prepared with directly heating-isothermal treatment method. It is indicated from the results that semi-solid billet with favorable microstructure can be obtained using this method without reheating, and treatment parameters permitted can be varied within a rather wider range. The grain microstructure obtained is better than that obtained with SIMA method. The mechanism is that the original casting grains are diminished greatly after the rod is extruded, and lots of aberrant inner energy is retained in the microstructures, which provides an inner driving force for the subsequent transformation of dendrites to spherical grains under high temperatures. It can be seen from the experimental results that when industrial extrusion rod of LC9 aluminum alloy is heated at 620℃, and held at that temperature for about 25min, perfect fine equiaxial grains can be obtained, and the average grain size is about 80μm.

Key words: directly heating-isothermal treatment; aluminum alloys; semi-solid; microstructure evolution