Study on New Heat-free Aluminum Alloy Materials for Integrated Die casting

Tesla Model Y successfully demonstrated the significant advantages of increased production efficiency, reduced production costs and shorter production cycle brought about by the integrated die-casting heat-free process (figure 1). Under the guidance of Tesla, the new car-making forces represented by Wei Xiaoli are actively laying out the integrated die-casting heat-free technology, which is expected to lead a new technological revolution in the automobile manufacturing industry. the first technical barrier to be broken through in the integrated die-casting heat-free treatment process is the development of new aluminum alloy materials, which is the basis of the integrated die-casting heat-free treatment process.

Fig. 1 Integrated large die casting

1 Application background of heat-free heat-free high toughness aluminum alloy by integrated die casting

1.1 advantages of integrated die casting process

The integrated die casting of large parts is a subversion of the traditional automobile manufacturing process, which ends the traditional automobile manufacturing method of stamping before welding, greatly reduces the process complexity, shortens the production cycle, and has a remarkable effect on lightweight and cost reduction. Specifically, the advantages of integrated die casting process.

(1) lightweight: making full use of the low-density characteristics of aluminum alloy on large-size structural parts is expected to greatly reduce the weight of the car body.

(2) improving efficiency and reducing cost: through one-time die-casting molding, the number of production lines of parts and components and the process of welding can be greatly reduced, thus the production cycle can be shortened.

(3) improve the strength of parts: integrated die casting avoids the reduction of strength caused by welding, and the factors such as installation hole and installation position can be ignored in the design of parts, so as to use a more optimized engineering structure.

1.2 difficulties in Integrated Die casting process

The large integrated structure can not be heat treated at high temperature, so there is an urgent need to develop a new heat-free high toughness aluminum alloy material to replace AlSi10MnMg, reduce the cost of heat treatment, and ensure that the material still has sufficient strength and toughness after forming.

2 material development of high toughness aluminum alloy without heat treatment

2.1 Technical requirements for heat-free high strength and toughness aluminum alloy materials

The aluminum alloy belongs to Al-Si series aluminum alloy. The introduction of Mn element can improve the demoulding effect of the material and counteract the adverse effect of Fe element. Several other trace elements are introduced to refine the grain and improve the strength. And material production allows the addition of a certain proportion of aluminum waste, which can reduce the carbon emissions of aluminum alloy production and help to achieve the goal of carbon neutralization as soon as possible.

2.2 Die casting process of high toughness aluminum alloy without heat treatment

Melting temperature: 730 ℃ ±10 ℃, degassing time: 10: 15 min, equivalent to AlSi10MnMg; die casting temperature: 700 ℃ 710 ℃, about 20 ℃ higher than AlSi10MnMg; die temperature: 120 ℃ 180 ℃ (according to the actual situation of the product); die casting parameters: please refer to the AlSi10MnMg parameters (according to the actual situation of the product).

2.3 process control

Melt purification degree (reducing slag and pore content), vacuum degree guarantee (mold sealing, vacuum exhaust), pre-crystallization control (molten cup aluminum temperature, barrel heating, die casting process).

2.4 material verification

(1) Test piece and flat die: mechanical property test (different natural aging time, baking process), welding, riveting, bonding, spraying, etc.

(2) small castings: damping tower, etc.; mechanical properties at different positions (different natural aging time, baking process); medium castings: subframe, rear longitudinal beam, etc.; mechanical properties at different positions (different natural aging time, baking process).

(3) large integrated castings: front engine room, rear floor, etc.; mechanical properties of different positions (different natural aging time, baking process).

2.5 process verification

(1) temperature: die casting temperature, mold temperature, etc.

(2) Speed: high speed, medium speed, etc.

(3) pressure: casting pressure.

(4) time: injection time, cooling time, pressurization time, etc.

3 properties of high toughness aluminum alloy without heat treatment

In order to evaluate the material properties of the new aluminum alloy, the aluminum alloy raw material manufacturer carries out tensile test pieces, plate die bulk sampling specimens and parts bulk sampling tests. in order to test the mechanical properties, metallographic structure, fracture morphology and fatigue properties of the material.

3.1 Mechanical properties of tensile test piece (steady state) (figure 2)

Fig. 2 Mechanical properties of tensile test piece

3.2 metallographic structure of tensile test piece (figure 3)

Fig. 3 metallographic structure of tensile test piece

3.3 sampling position and mechanical properties of plate mold bulk sampling (Fig. 4 ~ Fig. 6)

Fig. 4 sampling position of plate mold body

Fig. 5 Mechanical properties of flat plate mold

Fig. 6 fracture of flat die body tensile test piece

4 Application case of high toughness aluminum alloy without heat treatment

With the application of integrated die casting heat treatment free technology, because the structure of large products is more complex than that of small castings, the mechanical properties and process parameters of different parts may be very different, so before the production of new products, die casting enterprises need to deeply participate in the development and design process of integrated products according to the needs of customers. Optimize the die casting process parameters according to customer demand and raw material performance.

4.1 shock absorption tower-heat-free high toughness aluminum alloy

The die casting of the damping tower is shown in figure 7.

Fig. 7 physical shock absorber tower

The mechanical properties of the shock absorber body sampling are shown in figure 8.

(a) tensile strength

(B) yield strength

(C) elongation

Fig. 8 Mechanical properties of shock absorbers at different positions

4.2 Rear longitudinal beam-heat-free high toughness aluminum alloy

The physical object of the rear longitudinal beam die casting and the sampling position of the tensile test piece are shown in figure 9.

Fig. 9 rear longitudinal beam and sampling position

The mechanical properties of different castings are shown in figure 10.

(a) tensile strength

(B) yield strength

(C) elongation

Fig. 10 Mechanical properties of RGA castings with different serial numbers

The body of the rear longitudinal beam is sampled, and the mechanical properties of different parts are shown in figure 11.

(a) tensile strength

(B) yield strength

(C) elongation

Fig. 11 Mechanical properties of castings in different parts of RGA

The X-ray inspection results of the rear longitudinal beam are shown in figure 12.

Fig. 12 results of X-ray inspection

5 conclusion

Driven by the "Blue Sky Defense War" and "double carbon" policy, the development of automobile energy saving and emission reduction and low carbonization of the industrial chain is very urgent. the development of new aluminum alloy materials for integrated die-casting heat-free treatment provides a solid foundation for the optimization and expansion of integrated die-casting process for vehicle parts.

The development, testing, application and development trend of the new aluminum alloy with integrated die-casting heat-free treatment are deeply exchanged and discussed, which fully demonstrates its solid R & D capability and profound technology accumulation in the field of aluminum alloy raw materials. it shows the wide application of its raw materials in many industries, which brings inspiration to readers.

The follow-up vehicle, die-casting and raw material enterprises will work together to promote the application of integrated die-casting heat-free process in vehicle parts, so as to contribute to the early realization of carbon peak and carbon neutralization in the automobile industry.