Audi: Combined use of multiple materials, Q7 weight reduction by 300kg

By boldly using aluminum alloy and high-tensile steel plates in the body and chassis, the weight has been reduced by 300kg.

Masawa Okuyama, head of the technical training project of Audi Japan’s network development department, pointed out: “The car is designed in accordance with the principles of suitable materials, suitable places and suitable quantities, and is designed with various materials such as aluminum alloy and high-tensile steel plates, which has achieved substantial weight reduction. As a result, fuel efficiency has improved by more than 30%, and large SUVs have also achieved agile driving performance.”

First look at the car body, aluminum parts account for 41% of the total weight. Mainly the front end, rear end, cab exterior & shell and other parts that do not need to pursue high strength. Aluminum alloy is also used for the front fenders, engine cover and rear door.

The frame part adopts hot-forged steel plate, and the main frame part of the cab, such as the center pillar and floor longitudinal beam, adopts high-strength hot-forged steel plate. Hot forging generally refers to the technology of heating the steel plate to about 900°C, pressing it in a softened state, and at the same time using the cooling effect of contact with the mold to strengthen the quenching technology. It can achieve 1500MPa-level tensile strength and high dimensional accuracy. Through the above measures, the vehicle body alone was reduced by 71kg, and the door was also reduced by 24kg by using aluminum alloy.

The difficulty when using multiple materials is how to firmly join the different materials together. Okuyama said: “The joining of aluminum alloy and high-tensile steel plate uses friction stir welding and hollow rivets.” In addition, in the chassis, the weight of the suspension link is reduced by using aluminum alloy and high-tension steel plate, and the pivot bearing is also adopted. Aluminum alloy castings realize weight reduction. In this way, the overall weight of the chassis is reduced by more than 100kg. Audi has actively introduced cars with all-aluminum alloy bodies before. The large sedan “A8” launched in 1994 and the small car “A2” launched in 1999 are typical examples. However, the cost of aluminum alloy is higher than that of steel. In addition, due to the increase in the strength of high-tensile steel plates, manufacturing technologies such as hot forging have also been continuously developed. Recently, Audi has begun to devote itself to “material diversification” using multiple materials. Of course, such platform innovation requires huge investment. This is possible because Audi is a member of the Volkswagen Group and the platform developed can be used by the entire group.

Pursuing a balance between lightweight and cost, Q7 is the first car to adopt the latest general platform “MLB evo” of Volkswagen Group. Among the platforms of the Volkswagen Group, Audi “A3” and Volkswagen “Golf” adopt “MQB” (Modular Matrix for Horizontal Engine Vehicles), and MLB evo is a modular platform for vehicles with vertical engine. In addition to the Audi Q7, MLB evo is expected to be adopted by new models such as the mid-size sedan “A4”, the Volkswagen SUV “Touareg” and the Porsche SUV “Cayenne”. Okuyama pointed out, “Even if the vehicle type is different, the basic design can be common. Even the pedal height and axle are the same, but the overall size and suspension layout are changed according to the type of vehicle type. The Volkswagen Group produces 1.2 million to 1.3 million vehicles each year using MLB. Evo’s car, therefore, it is easy to recover the cost even if a huge investment is made.” In the context of the continuous strengthening of global environmental standards, automakers are accelerating the promotion of lightweight vehicles in order to improve fuel efficiency. However, it is very inefficient to invest only in certain types of models, so companies are accelerating the generalization of platforms. However, in order to develop a platform that supports a wide range of vehicle types from high-end to low-end, it is necessary to take into account lightweight and cost reduction. Therefore, Audi and Volkswagen are honing the technology of using a variety of materials in the group.