Prospects for Lightweight Structural Materials (Part One)

The main parts of aluminum alloy structural parts in the automobile industry are die castings. For example, cast aluminum alloy parts such as engine parts, gearbox parts and chassis parts are the main supply system. In the automobile parts, the deformed aluminum by rolling and extrusion is mainly used to produce radiators, aluminum doors and covers, anti-collision beams and other components. At present, aluminum castings account for about 75% of automotive aluminum alloy parts. Deformed products, especially rolled aluminum plates and body die casting structural parts are new growth points and have good development space.
 
The use of aluminum in the automotive industry
At present, the average amount of aluminum used in the automotive industry is 150 to 180kg, and all aluminum bodies and new energy vehicles can reach more than 400kg. According to a report by Ducker in 2018, the annual growth rate of aluminum alloy applications in automobiles exceeded 8%, and the average aluminum consumption per vehicle is expected to reach 220kg or more by 2025.
 
Aluminum alloy parts
At present, most automotive aluminum alloy parts adopt die casting process. For example, die casting engine blocks and low-pressure die casting wheels have formed related industrial chains. Related domestic industries are at the international frontier level. Taking the wheel industry as an example, there are a large number of wheels every year exporting from China to foreign countries. At the same time, China’s wheel industry has also set up factories abroad to reduce logistics and tariff costs. In addition, the level and scale of domestic powertrain component die castings are also the highest and largest, forming a large number of die casting enterprises in the Yangtze River Delta and the Pearl River Delta as the gathering area, which not only meets the demand for domestic auto parts, but also has a large export volume.
 
In terms of material types, chassis parts are all made from A356 (American grade) or AlSi7Mg (German grade). These parts all adopt low-pressure or gravity die casting process, and all parts require T6 heat treatment. The shell die casting parts of the power system mainly adopt the Al-Si-Fe series. The alloy types with the most application of these parts are A380 (American grade), AlSi9Cu3Fe (German grade) and ADC12 (Japanese grade), all of which are hypoeutectic series. The mass fraction of copper is between 2% and 4%, which can increase the yield strength to a certain extent, and the mass fraction of iron is between 0.8% and 1.3%, in order to solve the sticking problem in the die casting process. This kind of part does not require good elongation, generally less than 3%. The control requirements for alloying elements are relatively low, and can be produced from recycled aluminum. The body structure parts adopt Al-Si-Mn series, mainly AlSi10MnMg (German grade) and A365 (American grade). These parts are characterized by good elongation and strict alloy range requirements, and cannot be produced from recycled aluminum.
 
Starting from 2010, there has been a wave of vacuum die casting production of body structural parts in the world. Domestic die casting plants are mainly represented by foreign capital and joint ventures to produce large-scale vacuum die casting thin-walled parts for high-end car body structural parts. The main material of these parts is AlSi10-MnMg, and the main feature is that it requires ultra-high vacuum to meet T7 heat treatment and riveting performance (Solid solution and overaging) . It should be emphasized that the emergence of body structure parts has provided a great driving force for the demand, research and development of aluminum alloy materials. The main reason is that the existing vacuum die casting parts need heat treatment to obtain good elongation, which is used to be riveted with the surrounding body parts. Therefore, the yield of such part is not high. There are few high-quality suppliers, and the price is high. The R&D institutions of major international aluminum alloys and automobile companies are developing die-cast aluminum alloy materials that can be riveted without heat treatment for body parts, such as Magsimal-59 and Castduct-18 alloys from Germany Rheinland, Alcoa's C611 and A152 alloys, as well as A379 from the R&D Center of General Motors. At present, mass-produced non heat treated alloys have been commercialized. Because of the emergence of non heat treated alloys with good toughness, the cost and performance of body structural parts have greater advantages. With the rapid growth of large and complex structural components of new energy vehicles, this field will realize rapid development.
 
In addition, growth rates of aluminum alloy in automobiles for applications of rolled products used for four doors parts and two parts of covers are highest. Taking 6××× series aluminum plates as an example, they have already obtained more than 50% of the engine cover. Unlike die casting aluminum alloy parts, rolled products are mainly imported or produced by wholly foreign-owned enterprises. In terms of materials, automotive aluminum plates mainly include 5××× series with good formability such as 5182 and 5754. This type of aluminum alloy has no heat treatment strengthening characteristics and mainly produces complex formed parts for door inner panels. Another type 6 ××× series aluminum plates such as 6016 and 6061 have good age-hardening properties and are suitable for forming outer plates for four doors and two covers. Because of the complicated production and coating process of automobile outer panels, it is necessary to perfectly match the natural aging characteristics of the solid solution state or pre-aged state of 6××× series alloys, which is usually valid for half a year. Therefore, high requirements are put forward for 6××× series alloys for aluminum plate manufacturers and users.