An Automotive body depends on the manufacturer's considerations with the legislation and regulation, and some on the requirements of the customers. Most of the manufacturers prefer featured materials which are lightweight, economic, safety and recyclability.
The main elements of selecting material especially for the body is involved in a wide variety of characteristics such as thermal, chemical or mechanical resistance, manufacturing efficiency and durability. Steel stands as the first choice for manufacturers with all the required characteristics. The improvement or development in the steel industry made the steel stronger, lightweight and stiffer than the earlier. Steel includes not only vehicle bodies, but also engine, chassis, wheels and many other parts. Iron and steel develop the critical components of structure for the bulk manufacturing of vehicles and are low-cost.
The best reason for using steel as a body structure is its natural capability to absorb the impact energy produced in a crash.
Aluminium is widely used in the automotive industry, in chassis and body structure. Use of aluminium can possibly decrease the weight of the vehicle. Its low weight and high specific energy absorption and precise strength are its most significant characteristics. Aluminium is resistant to corrosion, but according to its low modulus of flexibility, it cannot substitute steel parts. Hence those parts need to be re-engineered to adopt the same mechanical strength.
Aluminium usage in the automotive industry has vastly grown within less period of time. In the automotive industry, aluminium castings have been used for pistons, cylinder heads, intake manifolds and transmission. In chassis applications, it is used as wheels, for brackets, brake components, suspension, steering components and instrument panels. Aluminium is used for body structures, finishing and exterior attachments such as crossbeams, doors or bonnets.
Latest improvements showed that 50per cent of the steel is saved for the body in white by the substitution of steel by aluminium. This can result in up to 20-30 per cent reduction in the total weight of the vehicle.
Magnesium is another light-weight metal that is growing increasingly next to aluminium in automotive engineering. It is 33% lighter than aluminium and 75% lighter than steel elements. Magnesium components have many mechanical disadvantages that need a unique design for utilisation to automotive products.
Magnesium has lower tensile strength, fatigue strength, and creep strength compared to Aluminium. The modulus and hardness of magnesium alloys are lower than aluminium, while the thermal expansion coefficient is greater. As it has low mechanical strength, pure magnesium cannot be used, must be alloyed with other components. The most common alloying components for room temperature applications is Mg-Al-Zn group, which include aluminium, manganese, and zinc.
As there is a high importance on greenhouse gas reductions, decrease of emission and improving fuel efficiency is the most important one for an automotive company. Lightweight metals can improve fuel effectiveness more than other factors. Experiments reveal that 10 per cent of weight reduction can lead to 6 to 8 per cent improvement in fuel usage. Weight reduction can be obtained in three ways:
• Substituting elements of high precise weight with moderate density materials without decreasing rigidity and durability. For example, replacement of steel with aluminum, magnesium, composites and foams.
• Optimizing the design of load-carrying elements and exterior attachments to reduce their weight without any loss in rigidity or functionality.
• Optimizing the production process, such as decreasing spot welding and arranging with new joining techniques.
Most important industry driven factor in the vehicle industry is the cost, which determines any new element has an opportunity to be chosen for vehicle components. It includes three major economic factors; the actual cost of raw materials, manufacturing added value, and the cost to design.
Aluminium and magnesium alloys are more costly than the currently used steel and cast irons. Since the cost is expensive, decisions to select light elements must be justified on the basis of advanced functionality. Meanwhile, the high cost is one of the major barriers in the use of composite materials.
Safety plays a major role in the automotive industry, the manufactured Body components and the chassis are ensured meeting the quality test. Safety plays a major role in the automotive industry, the manufactured body components and the chassis are ensured meeting the quality test. The two important safety measures in the automotive industry considered are crashworthiness and penetration resistance. In more detail, crashworthiness is the potential of absorption of the energy through controlled crash modes and mechanisms. Penetration resistance is concerned with the total absorption without allowing fragment piercing.
The most important concerns in automotive industries are ‘protection of resources’, ‘reduction of CO2 emissions’, and ‘recycling’. Europe and Asian countries have guidelines about the recyclability. The United States has no issues and regulations about automotive end-of-life. Steel material can be easily recyclable while the aluminium involves in high cost.