Investigation On Semi-solid Die-casting Process And Properties Of AZ91D Magnesium Alloy

The better prospects application of AZ91D magnesium alloy was investigated throughthe system of the alloy semi-solid slurry preparation and rheological die-casting process indetail. The organizational nature of the semi-solid slurry was obtained by controlling thesolidification of liquid metal cooling process enthalpy balance to optimize the processparameters. The better Microstructure and properties of AZ91D magnesium alloy parts wasobtained by using the obtained semi-solid slurry rheology die casting, optimization ofdie-casting parameters. The mechanical properties of castings was analyed after casting anddie casting the slurry.The results show as follows:The non-dendritic thixotropic organizational characteristics of semi-solid slurry can beproduced by the two sets of semi-solid slurry preparation devices independent design andassembly. The slurry performance which was prepared by second pulping process is batterthan the first one. Because the second pulping process uses the brass and metalliquid heatexchange through circulating cooling water at the rotating electromagnetic field. The thebest pulping process parameters of the second pulping process is electromagnetic stirringpulping current30A, frequency30Hz and casting temperature of580℃.The semi-solidslurry organizations and liquidity are better which the HBW of castings hardness values upto68.08under such conditions.The isothermal heat treatment experiments of semi-solid billet casting shows that thebillet microstructure and morphologies maintain the non-dendritic thixotropiccharacteristics which meets the conditions of thixoforming after heat treatments. Theresults of SEM, EDS and XRD analysis show that the experimental pulping processachieve the purpose of improving the material properties through changing the morphologyof primary phase of the slurry.The semi-solid slurry casting parameters has been systematically studied by usingHorizontal cold chamber die casting machine die-casting slurry. It is found that the surfacequality and mechanical properties of the die-casting parts are best, when the die-castingmachine handwheel degree of opening to1080℃, pouring temperature to585℃and thefilling time of3s. And the Brinell hardness of HBW is up to83.02, tensile strength of283.02Mpa, yield strength172.09Mpa,an elongation of4.8%. The results of the die-castsample after T4heat treatment show that the semi-solid die casting rheological test bar, the tensile strength, yield strength and elongation are certainly improved, but the hardnessvalues is decreased after the heat treatment.The SEM analysis of the fracture surfaces after stretching shows that fracturemechanism of the AZ91D magnesium alloy at different states is mainly intergranular brittlefracture,tough-off characteristic is not obvious. The main source of cracks are pores andinclusions in the die casting. The main defects appearing in the die casting areporosity,loose, burrs inclusions and so on. Improvement measures were proposed for thedefects.