Investigation On Rheo-rolling Strip Of AZ91D Magnesium Alloy

Magnesium alloy is the lightest metal structural material, which has many advantages of strength-to-weight ratio,excellent machine processing property,easy manufacturing and low processing cost,superior shock absorption and electromagnetic shielding than aluminum alloy, low melting temperature,low specific heat,low latent heat of solidification low kinetics viscosity, etc. All of these, can reduce energy consumption of melting,shorten the time of forming and processing,prolong the life of molds and equipments, moreover, can manufacture the thin-walled and complex structure parts. Semi-solid metal processing technical, synthesized the merits of liquid-casting technology and solid plastic forming technology, especially the Semi-solid rheo-forming technology, short process,high efficient energy saving, and can reduce the shrink by the solidification, and also can prolong the life of molds and equipments, because the part of latent of alloy liquid had been released. Horizontal twin roll casting process is the near-net shape forming and high efficient technology, and have the great potential applications. This is a challenge, with using the magnesium alloy, combine the Semi-solid metal process and twin roll casting process, where there will be more efficient more near-net shape,saving more energy.The series of experiments of rheo-rolling process was carried out on a horizontal twin-roll caster, and the Semi-solid slurry of AZ91D magnesium alloy was obtained by Low Superheat Pouring With a Shear Field(LSPSF), researched the parameters of inclined-rotary-tube pouring in prepare slurry,parameters of rheo-rolling process,the microstructure of Semi-solid influenced by the rolling-casting, and the microstructure and the hardness of the sheet in different parts, the results is as following:(1) We could obtain good microstructure and fine quality of AZ91D semi-solid magnesium alloy slurry when the pouring temperature was between 620℃to 650℃, rotating speed was 75rev/min, inclined degree was 25°, the preheated temperature of slurry vessel was between 550℃to 570℃, static time in slurry vessel was between 30 to 90 seconds.(2) There will be nucleated largely, the grains will grow up near the tube wall and divorced from the tube wall, and can survive largely, with the low temperature pouring, and shearing and stirring of rotating tube, by using LSPSF, then standing in the slurry vessel for ripening and spheroidizing.(3) When produce the 3.5mm sheet in rheo-rolling, we should ensure the nozzle temperature at 420℃, the temperature of casting-rolling is between 585℃to 591℃, the rotating speed of rolls is between 9rev/min to 11rev/min, thus can roll successfully.(4) After rolling, the primary particles became round, there occurs liquid segregation at the edge of sheet, and crystal orientation occurs on some crystal planes, shown the plastic deformation happened slightly, furthermore, Al and Zn solute a lot inα-Mg, because of rapid solidification in this process.(5) Along the rolling, the grain density at the head of sheet is lower than the middle and the posterior of sheet, and the hardness of the head of sheet is high than the middle and the posterior of sheet, but the difference is small.