Aluminum Sheet Applications For Automotive Industry

Aluminum is such a crucial material which is used extensively in various industries and especially automotive industry. It is used hugely for the automotive parts as hoods, trunk lids and doors as it has qualities like its light weight, durability and recyclability. Aluminum sheet suppliers are tremendously happy about its market share increasing continuously and it is the most commonly used alloy for automotive applications.

The mechanical properties it inherits are just apt for automotive body sheets and their specific properties make it great for the industry. They have relatively good formability and highly resistant to corrosion. With their amazing qualities for workability, they are prone to the formation of Lüders bands during forming and thus, they are used mostly for inner-panel applications.

Design Guidelines

Since, the design guidelines and requirements are quite strict, the aluminum sheet suppliers are quite careful of the fact that automotive closures must be panel bending stiffness and dent resistance. The elastic modulus of aluminum (70 GPa) is made about one-third that of steel (210 GPa). Thus, the parts previously designed for steel needs to be redesigned to achieve the same stiffness.

Another way to improve stiffness in aluminum is to increase the ribbing used in the product or increase the part thickness. For closures and body-structure sheets, the thickness should be increased by a factor of about 1.45:1.

Critical Material Parameters

There are some critical parameters of aluminum sheet suppliers look out for as aluminum differs from steel and it can affect the formability:

Elastic Modulus

Using elastic modulus, one-third that of steel and aluminum parts would experience more springback. This can be reduced by increasing the blank holder force, the amount of stretching and the sheet thickness. The forming operation must be optimized to ensure at least 2% stretch throughout the part.

Friction

Friction between the tool and the aluminum sheet by the aluminum sheet suppliers is expected to be higher compared to steel sheet as aluminum has a surface roughness (Ra) from 0.25 to 0.38 micron. Thus, in comparison, the Ra of steel sheet is about 0.63 to 0.88 micron. The smoother texture of aluminum requires dry, waxlike lubricants.

Formability

For the stamping of autobody parts, the lower formability of aluminum compared to steel can be offset by using technology such as local blank holder force control with multiple-point hydraulic cushions, advanced addendum design or warm forming. Present R&D efforts are focused on heating the sheet to warm forming temperature while keeping the dies at room temperature.

5182 and 5754 are the principal 5xxx series alloys which are used in autobody panels. 5754, on the other hand is also recommended for elevated temperature applications. There are other series of alloys which are great for ultimate tensile strength of 125 to 400 MPa. The alloys like 6022 and 6111 are often used for outer panels since they are precipitation-hardened and free of Lüders bands.