Research On Microstructure And Mechanical Properties Of Die-Cast Al-Mg Alloy With High Strength And Toughness

Die casting process is near-net shape processing technology with high efficiency, good economic indicator, high precision in dimension and good compatibility. It has reached a widespread utilization and rapid development in manufacturing industry. Die casting are now common used to produce the important parts for many products. Die-casting aluminum alloy is the most widespread used die-casting alloy, but it has been limited due to its bad toughness. Especially, it isn’t fitted to being used in auto and motor parts which own high toughness and strength to bear the force and impact. It is imperative for our country to develop a kind of new die-casting aluminum alloy of high strength and toughness. The simulation analysis and optimization on the die-casting technologies of standard samples for non-ferrous alloy is carries out in this paper. The chemical composition of die casting aluminum-magnesium alloy is optimized by using the orthogonal tests. Then shot parameters and artificial aging are study too.The Flow-3D software was employed to analyze and optimize the existed gating system of standard samples. Meanwhile, design and optimization of high vacuum die casting for standard samples were conducted. The results show that gas entrapment and liquid alloy back-flow occurred around the runner nearby the ingate during slow shot in the existing die casting process. And this phenomenon could be better when transition angle between the sprue and the runner is increased to30mm. Meanwhile tapered runner with overflow was adopted, the backflow and gas entrapment can be moved to the packet buffer. Air vent located in the side of the overflow can effectively eliminate the blockage of exhaust path among different samples, which ensures adequate exhausting time after the samples are filled completely. Therefore, the internal quality of the casting is improved.This research is conducted on die-casting aluminum-magnesium alloy material, and assesses the influence of the Mg, Si and Mn contents on mechanical properties of standard samples. The result shows that the optimum composition with5.4%Mg、2.0%Si0.77%Mn、Fe<0.20%can achieve the best mechanical properties. And the tensile strength, yield strength, elongation, and stiffness can be up to353.58MPa,204.53MPa,12.46%and 102.05HV5respectively.The influences of shot parameters, such as injection pressure, injection velocity and the position of slow/high shot transition on the inner quality and mechanical properties of the die-casting samples of optimum contents are also researched in this paper. The result shows that, when the injection pressure is100MPa with high-speed injection velocity, and the position of slow/high shot transition is at220mm. The samples possess good formations, dense microstructure without defects of shrinkage cavity and porosity. And the tensile strength, elongation can reach351MPa and13.77%respectively. Besides, this research also explores the influences of artificial aging treatment on the microstructure and mechanical properties of the die-casting samples. When the samples are heated to250℃for3hours then air cooling, the tensile strength, yield strength and elongation can be up to380.5MPa,246.9MPa and11.48%respectively.