Application of Aluminum Alloy in Automobile Manufacturing

The reason for the use of aluminum sheet material in automobile manufacturing is its combination of light weight and high strength. The strength of aluminum alloy is lower than that of steel, but the density of aluminum alloy is about 2.7g/cm³, which is about 1/3 of that of steel (the density of steel is 7.85g/cm³). Thicker specifications can make up for the lack of strength .

Application of Aluminum Alloy in Automobile Manufacturing

Aluminum sheet material is always an alloy, and aluminum alloys are classified by their alloy composition, identified by a four-digit number (See The Following Table). The first number in the alloy classification designates the group (i.e. the main alloying elements) and other numbers designate the specific alloy. The alloy is usually followed by a material temper code, specifying the thermomechanical treatment during production (O for tempered material, H for work hardened material, T for heat treated material).

Another important difference between aluminum alloys is their sensitivity to heat treatment. Heat-treatable alloys contain elements such as magnesium, silicon, copper, and zinc that are not readily soluble in aluminum at lower temperatures. When these elements are precipitated from the matrix, they form particles of strengthening material (for example, Mg2Si in 6xxx alloys), which increases the strength and corrosion resistance of the aluminum sheet.
Precipitation can occur during heat treatment or at room temperature. The latter is called natural aging. There is an optimum value for precipitation hardening; if the heat treatment lasts too long, the strength of the material decreases and the material becomes overaged.
Some alloys, like 6xxx (AlMgSi) and 7xxx (AlZnMg) age harden continuously for a long time, which limits their shelf life in terms of formability.

1xxx Series consists of commercially pure aluminum alloys. They are highly weather and corrosion resistant and have good formability (and weldability), but their low strength makes them unsuitable for body and chassis applications. They can be used for other components such as light reflectors.

3xxx Series alloys are stronger while maintaining high formability (and weldability) at low cost. Their strength levels are generally not sufficient for structural applications, but many 3xxx sheets are used indirectly in the form of aluminum brazing sheets (3xxx clad 4xxx), aluminum sheet for car is the main material used to manufacture heat exchangers for automotive applications.

Alloys in the 5xxx group are generally stronger than alloys in the 3xxx group because magnesium is a more effective strengthener than manganese (manganese is also added to the 5xxx alloys to further improve work hardenability). Work hardened 5xxx alloys are very strong and suitable for structural applications.
Among the 5-series alloy aluminum sheets, 5083, 5754, 5052 aluminum sheet, etc. are commonly used in automobile manufacturing.

6xxx Series alloys can be heat treated after forming to increase strength by precipitating Mg2Si. High shape accuracy and surface appearance make these alloys suitable for the production of profiles. Because heating reduces strength, special precautions may need to be taken when welding these alloys.

The 7xxx Series alloys can be precipitation hardened to very high strength levels; in fact the highest strength levels achieved in aluminum. Natural aging causes these alloys to increase in strength and decrease in ductility over time.

Article source: https://www.sciencedirect.com/topics/materials-science/aluminum-sheet