Billetless simple thixoforming process

Abstract

Two kinds of billetless thixoforming processes were devised in the present study. One process employed a cooling slope, and the other exploited low superheat casting. In the former process, molten metal was poured down an inclined cooling slope in order to generate the semisolid slurry. The semisolid slurry flowed and solidified into a die located at the bottom end of the slope. In the latter process utilizing low superheat casting, the melt was poured directly into the die and solidified. The need to produce an ingot for further processing by thixoforming can be eliminated since the molten metal can be shaped directly into the semisolid state by synchronizing the pouring into the die with the thixoforming operation. The size of ingot can be easily varied accordingly by appropriate choice of ladle and die. The cooling slope is a very simple, compact and cheap piece of equipment with low associated running costs. The primary crystals of test pieces generated in the course of this present study were spheroidal, and the general morphology of the ingot microstructures, when heated up to semisolid condition, was very similar to the microstructures obtained by conventional semisolid casting routes. The mechanical properties of test pieces produced from ingots cast in this present study were very similar to properties of products made by conventional thixoforming. Tensile strengths of 293 MPa and 15% elongation were obtained after T6 heat treatment.