Analysis of Aluminum Alloy Application Strategies in Automotive Body Structures

Reducing the weight of the body structure is key to achieving lightweight vehicles. Aluminum alloy, with its high specific strength, good corrosion resistance, formability, and connectivity, has become one of the preferred materials for body structure lightweighting. Currently, commonly used deformed aluminum alloys in automotive body structures include 5xxx and 6xxx series. The 7xxx series aluminum alloys are used less frequently due to cost reasons.

Table 1 Common Deformed Aluminum Alloy Grades and Properties for Automotive Body Structures

1.Audi e-tron

Audi e-tron is a typical model that transitioned from a previous generation steel body (approximately 18% aluminum alloy) to a steel-aluminum hybrid body (approximately 50% aluminum alloy). The Audi e-tron not only uses aluminum alloy materials extensively in its outer panels but also incorporates a certain proportion of aluminum alloy materials in its structural components. The main aluminum alloy sheet used is the 6xxx series, which accounts for 42%, as shown in Figure 1.

Figure 1 Material Proportion of Audi e-tron Body Structure

As shown in Figure 2, the most significant weight reduction effect of aluminum alloy in the vehicle body components is observed in the roof and cross beams, achieving a weight reduction ratio of 58%. The aluminum alloy upper body also reduced weight by 80.6 kg compared to the steel upper body.

Figure 2 Weight Reduction Effect of Aluminum Alloy Body Structure in Audi e-tron

Among the aluminum alloy components in Audi e-tron, the most typical and concerning aspect for designers is the aluminum alloy B-pillar and its corresponding crash safety results. The upper part of the B-pillar in Audi e-tron uses high-strength 6xxx aluminum alloy as the outer panel, 7xxx aluminum alloy as the inner panel, and the lower part uses laser welded 6xxx aluminum alloy. The B-pillar design achieves the same structural safety as hot-formed steel when responding to side impacts, which verifies the safety of this aluminum alloy B-pillar solution, as shown in Figure 3.

Figure 3 Aluminum Alloy Solution for Audi e-tron B Pillar

Figure 6 Comparison of Specific Strength of Different Material Solutions for Audi e-tron Roof and B-Pillar

2.Chevrolet Corvette

Compared to Audi e-tron, the application of aluminum alloy materials in Chevrolet Corvette has new characteristics, including the use of aluminum profiles, cast aluminum, and aluminum profile enhanced embedded structures.

Figure 7 Body Structure Forming Method Distribution of Chevrolet Corvette

1) Use of Aluminum Profiles.

As shown in Figure 7, the materials used in Chevrolet Corvette are primarily aluminum sheets and aluminum profiles. The use of aluminum stamped parts has decreased to some extent in C8 compared to C7, mainly due to the rising prices of aluminum sheets, while the use of aluminum castings has increased. At the same time, the use of aluminum profiles has consistently remained at 40%. One major reason is that the mold costs for aluminum profiles are significantly lower compared to aluminum sheets, and Japanese companies have long started their technological layout in aluminum profiles.

Figure 8 Use of Aluminum Profiles in Body Structure Framework

2) Use of Cast Aluminum.

For the tower structure in the body framework, which is a stress concentration point, higher crush strength and fatigue strength are often required. Using cast aluminum as the material for the tower structure can achieve higher strengths than steel due to the possibility of adding more reinforcement ribs in the design, as shown in Figure 9. More importantly, through casting processes, significant cost savings can be achieved in transportation, assembly, and connection, leading to better economic efficiency and lower carbon effects.

Figure 9 Use of Cast Aluminum

3) Enhanced Embedded Structures.

Due to the higher material costs of 7xxx aluminum alloys compared to 6xxx aluminum alloys, and the production efficiency being only one-third of that of 6xxx aluminum alloys, the most used aluminum profile in Chevrolet Corvette is still the 6xxx aluminum alloy. However, for the 6xxx aluminum alloy, the design of this model adopts enhanced embedded structures to achieve higher strength, as shown in Figure 10.

Figure 10 Use of Enhanced Embedded Structures for Aluminum Profiles