Study On Heat Treatment Process Of Deformed Mg-8.8Gd-3.5Y-1.5Nd-0.5Zr Alloy

Mg-Gd-Y-Nd-Zr alloy is considered great high temperature mechanical properties,casting properties, corrosion resistance, welding performance and so on, which is veryrepresentative of a class in rare earth magnesium alloy. Both T6treatment (solid solution andaging treatment) and deformation processing can improve the performance of the as-castalloy better. On the basis of the achievements of the prophase stage, this paper will be acombination of deformation treatment and T6treatment of Mg-8.8Gd-3.5Y-1.5Nd-0.5Zralloy.The research is systematically studying action rule of the effect on heat treatmentprocess on the micro-structure and microstructure and property of the alloy.First, the Box-Behnken experimental design is used to determine the range of keyprocess parameters of heat treatment process, which contains solution temperature,solutiontime,aging temperature,aging time. The solution treatment is chosen on the temperature of510℃,520℃,530℃,The time is8h,12h,16h.The aging treatment is chosen on thetemperature of200℃,225℃,250℃,The aging time is16h,20h,24h.The best parametersof heat treatment process for the deformation in the alloy is obtained by optimization design:510.38℃for8.49h and240.49℃for23h.Following optical microscopy (OM), tensile test on room temperature, scanning electronmicroscopy (SEM),and so on, we can analyze the influence of heat treatment of T6to thedeforming alloy from the micro-structure, mechanical performance and fracture analysis.After multiple forging, grain can refining obviously. Compared with the as-cast alloy, thetensile strength is increased about50％~90％, and the plasticity increases to4~6times.The solution time and aging temperature make a great effect to the alloy.After the T6heattreatment for510℃for8h and225℃for20h, the tensile strength reach290MPa,Elongation is4.8％.The precipitation of microstructure is great and homogeneousdistribution.The tensile fracture surface of the alloy is trending to ductile fracture,it belongs to quasi-cleavage fracture.510℃for8h and225℃for16h in T6solution, The tensile sample of the alloy show the result of cleavage fracture. By the increased time,the fracture morphology is trending to ductile fracture. The mechanical performance of ageing250℃for20h is showing theresult of quasi-cleavage fracture, and plasticity is improved obviously.