Semi-solid die-casting technology of aluminum alloy left suspension arm was studied, casting structural design, semi-solid die-casting process and bench testing were analyzed, and quality of sample products was tested. Semi-solid die-cast left suspension arm prototype passed bench test and achieved a weight reduction of more than 10% compared with gravity casting products.
Foreign countries have applied semi-solid die-casting technology to produce aluminum alloy castings earlier, and have already mass-produced new energy vehicle casing castings, such as air-conditioning compressor casings, front cross members, front and rear plug-in panels, battery casings, etc. Compared with foreign countries, domestic use of semi-solid die-casting technology to produce aluminum alloy castings is relatively late. In recent years, attempts have been made to apply it to new energy vehicles.
Aluminum alloy left suspension arm of car (hereinafter referred to as arm) is connected to motor and longitudinal beam. In addition to carrying a certain weight, it also plays a buffering and shock-absorbing role during operation of the car. Normally, arm castings are produced using a high-pressure casting process, which has advantages of high efficiency and low cost. High-pressure casting process used in design of arm casting structure of this project cannot meet static mechanical calculation requirements. Semi-solid cast aluminum alloy castings have higher mechanical properties. In order to meet requirements of stressed working conditions, research and development of semi-solid casting technology for arm was carried out.

According to boundary conditions and space constraints, arm casting structure design is carried out. Establish structural design model of support arm casting through CATIA software, use ABQUS finite element analysis software to perform calculation and verification analysis of first-order ground mode, calculation and verification analysis of Mises stress and maximum principal stress under extreme working conditions, calculation and verification analysis of Mises stress under typical working conditions. After multiple rounds of mold design (Fig. 1a) and modifications (Fig. 1b), as well as CAE calculation iterations, the first-, second-, and third-level ground modes, Mises stress and maximum principal stress under extreme operating conditions, Mises stress under typical operating conditions all meet design and CAE calculation standard requirements. Lightweight design of semi-solid die-cast aluminum alloy arm reduces weight by more than 10% compared with gravity-cast aluminum alloy arm.

 

Figure 1 Semi-solid arm casting design model and modified model

Perform multiple rounds of CAE calculation iterations. Calculate the first-order, second-order and third-order ground modes, Mises stress and maximum principal stress under extreme working conditions, and Mises stress under typical working conditions.
Standard requirement for ground mode is to be greater than 600 Hz, and calculation results of the first-order, second-order and third-order ground modes all meet this requirement (Figure 2).

 

Figure 2 Calculation of semi-solid arm's ground mode
Standard requirements for Mises stress and maximum principal stress in ultimate working condition are less than 85% of material's tensile strength and less than 75% of material's yield strength respectively, and calculation results all meet this requirement (Figure 3a-b). Mises stress standard requirement under typical working conditions is less than 75% of material yield strength, and calculation results meet this requirement (Figure 3c).

 

Figure 3 CAE calculation of semi-solid arm casting

Design, overflow and exhaust design of semi-solid die-casting pouring system of aluminum alloy arm are shown in Figure 4. Gating system is designed near bending position of casting, and inner runner is thicker, which is beneficial to filling and feeding of casting. Overflow and exhaust are designed at both ends far away from center of casting, overflow and exhaust systems at both ends are connected together to discharge outward.

 

Figure 4 Semi-solid die casting pouring system, overflow and exhaust design

Sigmasoft Virtual Molding software was used to numerically simulate semi-solid die-casting filling and solidification process of aluminum alloy arm. Results are shown in Figure 5.
As shown in Figure 6.

 

Figure 5 Numerical simulation results of semi-solid arm mold filling process

 

Figure 6 Numerical simulation results of solidification process of semi-solid arm
As can be seen from Figure 5, filling of semi-solid metal is smooth and smooth without splashing.
It can be seen from Figure 6 that support arm can achieve sequential solidification, and possibility of shrinkage porosity in support arm is very small.

Semi-solid die-cast aluminum alloy material is A319 aluminum alloy. Semi-solid arm casting is shown in Figure 7. The overall dimensions are 190 mm * 150 mm * 110 mm, with a wall thickness of 10 mm in the thinnest part and 33 mm in thicker part. As can be seen from Figure 7, appearance quality of casting is good and there are no wrinkles.

 

Figure 7 Semi-solid arm sample

X-ray flaw detection results of arm sample are shown in Figure 8. It can be seen from figure that there are no defects inside casting.

 

Figure 8 X-ray flaw detection results
Mechanical properties: Semi-solid die-cast A319 aluminum alloy material (body sampling) tensile strength 370 MPa, yield strength 323 MPa, elongation 4.6%, hardness HB128.
Microstructure: It can be seen from Figure 9 that α-Al primary crystal structure in microstructure of semi-solid die-cast arm (body sampling) is not common dendrites but degenerated dendrites, like petals (Figure 9).

 

Figure 9 Casting microstructure

Bench test of semi-solid die-cast arm sample includes: bench pull-out force test, bench fatigue test and bench destruction test. Sample passed above bench test, and results are shown in Figure 10.

 

 

Figure 10 Bench test

(1) A semi-solid die-casting process for A319 aluminum alloy arm was developed, and developed sample passed bench pull-out force test, bench fatigue test and bench destruction test.
(2) Compared with gravity casting products, aluminum alloy arm castings formed by semi-solid die-casting process reduce weight by more than 10%.
(3) Sample testing was taken from semi-solid die-cast arm sample body. Tensile strength is 370 MPa, yield strength is 323 MPa, elongation is 4.6%, and hardness is greater than HB128.