In order to promote the adoption of aluminum body panels, it is necessary to provide for the potential panel shapes and the low-cost materials required by automobile manufacturers. It is important to improve material properties as well as forming and joining technologies, so as to be able to manufacture suitable body panel shapes. On the other hand, it is necessary to minimize the number of manufacturing processes, and to be able to use recycled aluminum alloys to ensure a low-cost material.
Aluminum Alloys
The important properties required for body panels are as shown in Table 2.3. Especially, it is necessary to improve the formability to enable, for example, hem flanging and stretch-forming for outer panels, and deep drawing for inner panels. It is important to be able to decrease strength before forming, and then redevelop high strength after paint baking under conventional baking conditions.
Figure 2.3 shows a study of the bake-hardening properties of 6xxx alloys after pre-aging. The specimens are solution heat treated at a high Temperature of 530°C and then water quenched, a conventional manufacturing process for aluminum body panels. Pre-aging is conducted at 50°C to 100°C immediately after water quenching. After one week at room temperature, the specimens are then heat treated using several different baking conditions
The pre-aged specimens have high strength after paint baking at low temperature for a short time compared with more conventional specimens. The improved bake-hardening properties are caused by fine precipitates of β’ − Mg2Si. This study is important in indicating how to improve the
material properties.
Forming Technology
It is not easy to promote the adoption of aluminum body panels just by improving the material properties. It is also important to provide optimum forming technologies for manufacturing the aluminum body panels. For example, tooling and forming conditions both need to be optimized. In addition, many kinds of forming technologies, such as hydro-forming. hot-forming and extreme cold-forming, need to be studied. Kobe Steel is investigating the optimization of tool and forming conditions using practical pressing studies and finite element (FEM) analysis. Figure 2.4 shows the 1400-ton Kobe Steel test press for manufacturing aluminum body panels. Useful data for aluminum body panels compared with conventional steel panels can be achieved by using direct experimental
pressing studies.
On the other hand, Figure 2.5 shows the relationship between finite element analysis and practical press forming.7 The prediction of cracks using finite element analysis corresponds with the results of cracks occurring during experimental press forming. The precision of finite element analysis will improve with increased applications, and this will play an increasing role in promoting adoption of aluminum panels.
Recycling
Aluminum alloys have excellent recycling properties. It is well-known that used aluminum beverage cans can be returned to new beverage cans. In Japan in 2001, the recovery ratio of used aluminum beverage cans was 83%, with a can-to-can ratio of 68%, the rest being used mainly for castings. Recycling of aluminum alloys is useful for reducing the cost of the aluminum material, and leads to improved life-cycle assessment. Therefore, the reuse of aluminum alloy body panels needs to be studied. In the case of aluminum press scrap, aluminum manufacturers can reproduce the same alloy sheets. However, in the case of aluminum scrap from a scrapped car, it is not easy to recover the same alloy sheet, because of the mixing of different alloys, such as 6xxx, 5xxx, and Al-Si series alloys, and different metals, such as aluminum and steel. Therefore, aluminum manufacturers have to work on alloy designs suitable for recycling and construction of a viable recycling system. The final target will be car-to-car.
Figure 2.6 shows the effect of using an aluminum Audi ASF car on saving energy. Energy saving from an all-aluminum car will be excellent compared with conventional steel cars, with the introduction of recycled aluminum alloys.
Aluminum Alloys
The important properties required for body panels are as shown in Table 2.3. Especially, it is necessary to improve the formability to enable, for example, hem flanging and stretch-forming for outer panels, and deep drawing for inner panels. It is important to be able to decrease strength before forming, and then redevelop high strength after paint baking under conventional baking conditions.
Figure 2.3 shows a study of the bake-hardening properties of 6xxx alloys after pre-aging. The specimens are solution heat treated at a high Temperature of 530°C and then water quenched, a conventional manufacturing process for aluminum body panels. Pre-aging is conducted at 50°C to 100°C immediately after water quenching. After one week at room temperature, the specimens are then heat treated using several different baking conditions
material properties.
Forming Technology
It is not easy to promote the adoption of aluminum body panels just by improving the material properties. It is also important to provide optimum forming technologies for manufacturing the aluminum body panels. For example, tooling and forming conditions both need to be optimized. In addition, many kinds of forming technologies, such as hydro-forming. hot-forming and extreme cold-forming, need to be studied. Kobe Steel is investigating the optimization of tool and forming conditions using practical pressing studies and finite element (FEM) analysis. Figure 2.4 shows the 1400-ton Kobe Steel test press for manufacturing aluminum body panels. Useful data for aluminum body panels compared with conventional steel panels can be achieved by using direct experimental
pressing studies.
On the other hand, Figure 2.5 shows the relationship between finite element analysis and practical press forming.7 The prediction of cracks using finite element analysis corresponds with the results of cracks occurring during experimental press forming. The precision of finite element analysis will improve with increased applications, and this will play an increasing role in promoting adoption of aluminum panels.
Recycling
Aluminum alloys have excellent recycling properties. It is well-known that used aluminum beverage cans can be returned to new beverage cans. In Japan in 2001, the recovery ratio of used aluminum beverage cans was 83%, with a can-to-can ratio of 68%, the rest being used mainly for castings. Recycling of aluminum alloys is useful for reducing the cost of the aluminum material, and leads to improved life-cycle assessment. Therefore, the reuse of aluminum alloy body panels needs to be studied. In the case of aluminum press scrap, aluminum manufacturers can reproduce the same alloy sheets. However, in the case of aluminum scrap from a scrapped car, it is not easy to recover the same alloy sheet, because of the mixing of different alloys, such as 6xxx, 5xxx, and Al-Si series alloys, and different metals, such as aluminum and steel. Therefore, aluminum manufacturers have to work on alloy designs suitable for recycling and construction of a viable recycling system. The final target will be car-to-car.
Figure 2.6 shows the effect of using an aluminum Audi ASF car on saving energy. Energy saving from an all-aluminum car will be excellent compared with conventional steel cars, with the introduction of recycled aluminum alloys.
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