Aluminum Alloy for Automobile

Introduction of Aluminum Alloy for Automobile

1.Hang-on parts

The boot lid (UK) or decklid (US) is the panel that covers the boot (or trunk) of an automobile. It enables access to the main luggage compartment. A hinge allows the boot lid to be raised, while devices such as springs or gas cylinders hold it up in the open position.

In principle, boot lids have to fulfil similar requirements and are subject to the same design guidelines as bonnets. However, aluminium sheets are used much less for boot lids than for bonnets. The main reason is that the “value” of weight saved in the rear of the car is significantly lower than in the front because of the aim for a 50:50 axle load distribution. In many cases, automobile engineers are even shifting mass (e.g. batteries) towards the back in order to achieve a more balanced axle weight distribution.

Aluminum alloy back door of car

Consequently, aluminium boot lids are mainly used for car models with an all-aluminium body structure. But there are nevertheless a few (mixed material design) upper car models which use an aluminium boot lid for weight reduction. When substituting aluminium for steel in a boot lid, weight savings of about 50% can be achieved. As an example, the boot lid shown below (weight 8.6 kg) – which was designed for the Ford P2000 vehicle – represents a weight reduction of 5.4 kg (53%) compared to an equivalent steel design. The alloy AA 6022-T4, aged to T6 during paint bake process, was applied. The thickness of the outer and inner panel of the bonnet and the boot lid was similar (0.85 mm)

An interesting example is the boot lid shown below which is made from the alloy TopForm®SPF. This is an AlMgMn alloy optimized for the superplastic forming process with a composition corresponding to the alloy EN-AW 5083. The alloy offers an ultra-fine grain structure as a result of special processing conditions during casting, rolling and heat treatment.

More important is the application of aluminium sheets for liftgates (or rear hatches) and tailgates, i.e. the doors or “gates” at the back of SUVs, hatchbacks, station wagons andsimilar type of vehicles. Liftgates and rear hatches are hinged at the top and open upwards, tailgates are lateral opening doors which are hinged at the left or right side. They greatly benefit from a reduced weight due to easier handling. In addition, a reduced weight cantranslate into significantly lower rear axle loads (as these panels overhang the rear axle) and hence additional seating capacity.

An early example of an aluminium liftgate is the GMT 830 liftgate. It was an all-aluminium design using EN-AW 6111-T4PD for the outer panel, EN-AW 6111-T4P for the reinforcements and EN-AW 5182-O for the inner panel. The aluminium liftgate was stamped using conventional press tools. The gauge of the outer panel was selected to meet the denting and oil-canning requirements. The aluminium liftgate was assembled using resistance spot welding and hemming. Coated steel nuts were used for hinge and latch attachments.

For the outer panel of the Saab 9-3 liftgate, the alloy EN AW-6016 has been used (t = 1.0 mm). The inner panel is made from the alloy Hydro 5182-M ssf (t = 1.2 mm), a special quality of the annealed O-temper EN AW-5182 (“stretcher-strain poor and/or stretcher-strain free”). In the “stretcher-strain free” condition, the formation of stretcher strain marks of the type A issuppressed by a small pre-deformation of the annealed sheet (at expense of the remaining formability). However, as soon as the strain level increases above 5 to 7 %, the fine striations of the Lüders lines of type B with a surface roughness depth < 1 0 μ m cannot be avoided. Therefore, “stretcher-strain free” AlMg alloy qualities have not found significant practical application.

An interesting lightweight design variant exhibits the tailgate of the VW Lupo 3L (produced 1999 – 2005), a special edition made with the intention to consume only 3 l of fuel per 100 km. The solution chosen for the tailgate included an integral magnesium inner part and an aluminium outer panel (as well as aluminium lock reinforcements) with a weight of 5.4 kg (compared to 10.5 kg for the steel solution). The aluminium outer panel is flanged over the magnesium inner part. In addition, adhesive flange bonding is used for strength and insulation. To avoid any potential of contact corrosion, the magnesium die casting is coated before assembly.

A cost-efficient lightweighting option is also the application of aluminium castings for the frames of back windows (see below).

2 Wings

Wings (UK) or fenders (US) denote the car body part that frames a wheel well (the fender underside). Its primary purpose is to prevent sand, mud, rocks, liquids, and other road spray from being thrown into the air by the rotating tire.

The term “wing” usually refers only to the panels over the front wheel arches since in modern cars, the rear “wings” are rather an integral part of the car’s side wall. The industry changed from rear wings bolted onto the quarter panel (a body panel which extends between the rear door and the trunk) to an enlarged quarter panel that fulfilled both functions and ultimately to a one-piece side wall. Today’s state-of-the-art is a one-piece side wall; the quarter panel is used in those cases where the production of a one-piece side wall is not feasible for technical reasons.

Introduction of Aluminum Alloy for Automobile

In general, wings are relatively simple components and a conversion from steel to aluminium does not present any difficulties.

The basic requirements for aluminium wings are largely identical with those for the outer panels of bonnets or boot lids, i.e.:

• – stiffness – determined by design and sheet thickness (generally 1.4 x steel sheet thickness),
• – buckling resistance – determined by sheet thickness, yield strength and design,
• – dynamic denting (stone chipping) – determined by sheet thickness and yield strength,
• – surface quality – determined by alloy type (preferably of the AlMgSi series), surface roughness and microstructure,
• – small hemming radius

Today’s standard aluminium alloys for outer body applications of the EN-AW 6xxx system fulfil all the requirements for standard wing designs. The resulting weight reduction compared to steel is normally slightly more than 50 %, i.e. the substitution of steel by aluminium for the wings offers attractive weight reduction possibilities in the front of the car. However, the market penetration of aluminium for wings is significantly lower than for bonnets. The main reason is that in many cases, plastic or fibre reinforced plastic wing panels are used. The advantage of plastic materials is the lower sensitiveness of plastics against minor parking damage (e.g. scratches and small dents).

But there are also car models where wings of highly complex shapes are required. An interesting solution for these special cases offers the superplastic forming technology.

3 Doors

The door allows entering and exiting the vehicle. The doors can be opened manually, or electrically powered. A conventional car door is hinged at its front-facing edge, allowing the door to swing outward from the car body. This type of door has the advantage that if it is opened during forward motion of the vehicle, the wind resistance will work against the opening door, and will effectively force its closure.

But depending on the type of car, there are also other door concepts in use:

Rear-hinged doors make entering and exiting the vehicle much easier. However safety concerns prevent the use of “suicide doors” today. On modern vehicles, the exceptions are rear-hinged back doors in combination with front-hinged front doors, mainly on chauffeur driven cars, taxis and MPVs.

Scissor doors are automobile doors that rotate vertically at a fixed hinge at the front of the door, rather than outwardly as with a conventional door. This type of doors is used on some exclusive sports cars (e.g. some Lamborghini models)

Butterfly doors are a type of door also seen on high-performance cars (e.g. the McLaren F1 supersportscar). They are similar to scissor doors, but while scissor doors move up, butterfly doors also move outwards, which makes for easier entry/exit at the expense of saving space.Gull-wing door describe car doors hinged at the roof rather than the side. They are found only on selected sports car models.

Aluminum alloy car door

Sliding doors open by sliding (usually horizontally), whereby the doors are either mounted on or suspended from a track. Sliding doors are most commonly used for minibuses (MPVs) to provide a large entrance or exit for passengers or without obstructing the pavement. They are also often used on the side of commercial vans as this allows a large opening for cargo to be loaded and unloaded without obstructing access.

However, the car door is not a simple hang-on panel but rather a structural module which fulfils many different functions. Basically, the door consists of an outer panel supported by an inner structural element where various additional components are attached. Furthermore, modern car doors usually include a reinforcing element (“side impact beam”) which protects the driver and passengers in case of a side impact, e.g. when smaller cars are struck by a larger SUV.
The door shell, the most visible component of a car door, holds all door parts together. The most important additional parts integrated into the door are:

• – Hinges: The hinges connect the door to the body structure, allow opening and closing of the door and keep the door in the necessary position to close properly.
• – Door handle and lock: These parts allow the door to close securely and prevent it from opening. There are a variety of car door locking systems. Newer cars contain a power lock feature that allows drivers to remotely lock all doors. The door handles are on the inside and outside of the car door.
• – Windows and window regulator: Vehicle doors have generally windows and most of these may be opened to various extents. Generally, car door windows retract downwards into the body of the doors. The window regulator is the mechanism found inside the car door that raises and lowers the window glass. The windows are opened either with a manual crank, or switchable electrical motor.

In addition, there is in general an interior door panel which is an important styling component for the interior, but also contributes to the functionality and ergonomics of the car. It holds various interior parts like the interior door handles, armrests and/or storage trays, switches, and lights. The door body may also house noise dampening mats, electronic systems like the window controls and locking mechanism, loudspeakers or airbags as an additional protection in case of a side impact, etc.