Experiment on rheo squeeze casting of aluminum alloy

Cast aluminum alloy, with good flow filling performance, wear resistance, and good dimensional stability, make its casting performance is good, automobile, motorcycle engine and related industrial fields have been widely used. Aluminum alloy is used in automobile engine to make cylinder block, which has the advantages of better heat dissipation and lighter weight than cast iron. The engine piston made of aluminum alloy, because of its small linear expansion coefficient and good wear resistance, makes the engine work smoothly and greatly improves the working efficiency of the engine. Modern automobile, aviation manufacturing also pursue lightweight, low energy consumption and environmental protection requirements are increasingly high, how to make aluminum alloy in automotive, aviation and other industrial fields to promote a large number of applications, but also need to have a lower manufacturing cost, better comprehensive performance of aluminum alloy manufacturing process. Therefore, combined with the LSPSF semi-solid pulping process developed in the laboratory, A356 aluminum alloy casting was selected for rheological extrusion casting, and the manufacturing process of A356 aluminum alloy component was explored to achieve the goals of high material utilization rate, low cost, good comprehensive mechanical properties, energy saving and high efficiency.

Rheological extrusion casting (RCQ) is a near net forming casting method to obtain high quality castings by forming and solidifying semi-solid metal melt under high pressure. The castings formed by extrusion casting process have good characteristics such as compact structure, not easy to be involved in gas, reduction of cracks and higher dimensional accuracy of the parts. There are two kinds of pressing methods in squeeze casting: direct punch extrusion and indirect punch extrusion. Direct punch extrusion requires precise casting and can produce simple parts. Indirect squeeze casting is similar to die casting, but the section of the injection system is larger, and the greater pressure is transferred during solidification, which reduces gas involvement and makes the structure more compact. Squeeze casting parts can be strengthened by heat treatment such as solution aging. In this chapter, rheological indirect squeeze casting of A356 alloy was experimentally analyzed.

The alloy used in the experiment is A356 aluminum alloy which is commonly used in industry. A356 alloy has good hardness and strength, good casting performance and flow filling performance. It is widely used in automobile, motorcycle, aviation and other industries. At the same time, it is also one of the most used alloys in semi-solid processing for commercial production. A356 belongs to Al-Si-Mg series, which is a kind of high strength cast aluminum alloy with excellent comprehensive performance. It is widely used in automobile and motorcycle wheel hub, shell, multi-connection suspension frame and other parts. After determining the composition of the alloy (mass fraction, wt%), the temperature range of the solid and liquid phase of the alloy is 572~614℃. A356 alloy has the following characteristics:

(1) the Si content is relatively high, is a typical Al-Si-Mg ternary alloy, good fluidity, linear shrinkage, no hot crack tendency, can be made of thin wall and complex shape castings.

(2) It can be strengthened by heat treatment to form a strengthening phase Mg2Si, which can achieve better plasticity, high impact toughness and high strength. It is the preferred material for automotive wheel lightweight and energy saving.

(3) In the Al-Si-Mg ternary alloy, Mg2Si is a stable compound, and the equilibrium microstructure of A356 alloy is primary α+ eutectic (α+Si) +Mg2Si. During non-equilibrium solidification, impurity phases such as α (Fe3Si2Al12), β (Fe2Si2Al9) and Al8Fe MgSi6 may be formed. These needle impurity phases will destroy the continuity of the alloy matrix and seriously affect the mechanical properties of the alloy.

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