Aluminum alloys are widely used in industry due to their good formability, processability, weldability and very good corrosion resistance. Aluminum consumption in electric vehicles will continue to increase in coming years, reflected in body parts and battery containers. Battery casing is made of die-cast aluminum alloy parts, such as AlSi10MnMg alloy parts. Different researchers have found that aluminum alloy high-pressure die casting is particularly suitable for integral forming of integrated parts. Fe is inevitably introduced during smelting and casting processes, especially when scrap and recycled materials are used. Fe is a favorable element for improving mechanical properties in Al-Mg and Al-Mg-Mn alloys. Fe significantly increases yield strength of alloy, but significantly reduces elongation. Some studies have also found that increasing Si content improves strength of cast alloys, but reduces hardness and plasticity of aluminum alloys. Research shows that low pressure and low temperature increase porosity, promote formation of iron-rich intermetallic compounds, change morphology of α-Al phase, and deteriorate mechanical properties of alloy. Interaction between die-casting process parameters and alloy elements has a significant impact on alloy tensile properties.
At present, main research on influence of alloy elements and die-casting process conditions on mechanical properties focuses on short-term production processes. Considering unique use environment of parts, there are few reports discussing impact of long-term thermal environment on mechanical properties of aluminum alloys. Therefore, this study compares mechanical properties of AlSi12(Fe)(a) alloy and AlSi10MnMg alloy samples after heat treatment at 500h*120℃, studies mechanical property stability of thin-walled aluminum alloy high-pressure die castings in long-term thermal environments. It can provide reference for design and optimization of thin-walled die-casting parts for new energy vehicles. Samples pretreated at 500h × 120℃ and ordinary samples were selected for mechanical property testing. Although mechanical properties of AlSi12(Fe)(a) alloy sample changed after pretreatment, they did not decay below material standard value. After pretreatment, tensile strength and yield strength of AlSi10MnMg alloy sample increased, but elongation decreased and was lower than standard value of material.
In preparation stage, unified trial production conditions are adopted, die-casting process parameters are adjusted according to actual production conditions, and aluminum alloy liquid is die-cast from same batch of molten aluminum alloy as die-casting parts. Non-clamped parts should be free of defects such as scratches, pitting, cold insulation, cracks, inclusions and surface holes. Both ends should be polished smooth, feed port and slag bag port should be removed. See Figure 1 for a schematic diagram of dimensions. According to requirements of delivery state of parts, no heat treatment is used. Die-casting machine model is UB350iC, aluminum liquid pouring temperature is (680±10)℃, mold temperature machine temperature is (200±10)℃, vacuum degree is (40±10)kPa, and casting pressure is (95±10)MPa . A FED-720 oven was used for pretreatment, pretreatment parameters were 500 h × 120℃, and mechanical properties were tested. Environmental conditions of laboratory were set to (23±5)℃ and (50%±25%) (Rh is temperature), 6 AlSi12(Fe)(a) alloy test rods and 6 AlSi10MnMg alloy test rods were tested respectively. Among them, test rods No. 1 to No. 3 of AlSi12(Fe)(a) alloy and No. 1 to No. 3 test rods of AlSi10MnMg alloy were not pretreated; test rods No. 4 to No. 6 of two alloys were pretreated. Use K2012967 digital display vernier caliper to measure diameter of circular section in the middle of test rod, and use E45.305 electronic universal testing machine to test mechanical properties of test rod.

Table 1 Chemical composition of test alloy (%)

 

Figure 1 Schematic diagram of tensile specimen dimensions

 

Figure 2 Mechanical properties of AlSi12(Fe)(a) alloy

 

Figure 3 Mechanical properties of AlSi10MnMg alloy

Table 2 Mechanical properties of AlSi12(Fe)(a) alloy

Table 3 Mechanical properties of AlSi10MnMg alloy

It can be seen from test results in Table 2 and Table 3 that mechanical properties of material before pretreatment comply with DIN EN 1706 standard. After pretreatment, although mechanical properties of AlSi12(Fe)(a) alloy decreased, they still met requirements, but elongation of AlSi10MnMg alloy was lower than DIN EN 1706 standard.
AlSi12(Fe)(a) alloy is a eutectic Al-Si alloy with high thermal conductivity and good fluidity. It has excellent casting formability and can form complex thin-walled parts, which can meet production requirements of new energy vehicle battery components. Heat treatment process of AlSi10MnMg alloy will cause casting deformation and surface blistering problems. Especially as volume of die castings increases, it is difficult to reshape parts. Therefore, on the one hand, non-heat treatment die-casting aluminum alloy process can be used directly in as-cast state to avoid above problems. On the other hand, reducing heat treatment process of parts can also reduce manufacturing cost of parts.
Batteries generate more heat when running at high power. Therefore, application of new materials and structural optimization design have become the key to improving heat dissipation capacity of new energy vehicle battery modules. Because aluminum alloy has good thermal conductivity, processability, low cost, environmental protection and low density, it can achieve miniaturization and lightweight of new energy vehicle battery modules while maintaining high heat dissipation capacity of new energy vehicle battery modules. It is widely used in radiators, load-bearing plates, brackets, junction boxes, front covers, and other new energy vehicle parts.