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Over the past several decades, significant gains in automobile fuel efficiency have been achieved through down-sizing, aerodynamic design and drive train improvements. As performance limits are approached in these areas, aluminum is being used to further reduce body weight by up to 40% compared to steel. In anticipation of the continued demand for more fuel efficient automobiles, aluminum sheet component unibody and extrusion and cast component space frame designs have been studied to address joining and structural performance. Joint geometries unique to specific body designs clearly illustrate the need for close linkage of the design and assembly functions. Joining and assembly methods that provide static and dynamic structural integrity, 15 to 20 year durability and that can be integrated into robust manufacturing systems are key to aluminum usage for auto body structure.

The advent of high speed computers permits the use of the finite element method to model complex sheet metal forming processes on a reasonable time scale. The design and development of sheet metal parts in the automotive industry and the need for improved sheet forming processes and reduced part development cost have led to the use of computer simulation in tool/die design of sheet metal pressings. An accurate constitutive description of plastic anisotropic yield loci and work hardening of material behavior in sheet forming is now a reality. The constitutive equation developed at Alcoa for describing anisotropic material behavior is consistent with polycrystalline plasticity, and it is expected to improve the computational accuracy of forming process for polycrystalline metals and alloys.

Different scenarios for aluminum usage in automotive body structure are examined with emphasis on the potential effects on recycling. Alloy selection issues are addressed with regard to the limits on absorption of recycled automotive scrap into new cast or wrought products. The difference between “open loop” and “closed loop” recycling is discussed. Possible impacts of increased aluminum usage on the needs for separation technology and recycling infrastructure are reviewed briefly.

The need to substantially reduce the weight of automobiles to improve performance or meet CAFE requirements has led to an increased use of lightweight materials such as aluminum. To use aluminum efficiently in auto body structures, component and joint designs and joining methods are likely to differ from those traditionally used in steel bodies. With proper design, aluminum automotive frames can efficiently meet or exceed the performance requirements for stiffness, static strength, fatigue strength and crash performance. This paper presents some joint design concepts for aluminum frames and compares the performance of joining methods such as resistance spot welding (RSW), gas metal arc (GMA) welding, weld bonding, adhesive bonding, riveting and mechanical clinching for both unibody and spaceframe construction. Recommendations for preferred joining methods are also made based on the effect of design details on joint performance and assembly.

Determination of forming limit diagrams (FLDs) by experimental methods requires a significant amount of time and expertise in interpretation of data. Their construction can be especially difficult for aluminum alloys due to slightly negative or near zero strain rate sensitivity characteristics which create sharp strain gradients. For this reason a mathematical model which incorporates microstructural attributes, namely crystallographic texture, with a description of strain hardening behavior was developed by Barlat1 to predict the forming limit strains for a given material. Using Barlat, forming limit diagrams were predicted for various automotive body sheet alloys and verified against experimental data. Excellent correlation was found between the experimental and predicted diagrams. Prediction of limit strains requires approximately one-tenth of the time required for experimental diagrams and eliminates variations associated with experimental determination techniques.

Finite element modeling of sheet forming processes for complex automotive parts using an explicit dynamic code such as LS-DYNA3D is increasingly used for producibility analysis and die development. In modeling sheet metal forming processes, it is very common to represent material behavior by either Von Mises' or Hill's yield criterion using commercial finite element codes. However, these criteria do not provide an accurate representation of aluminum alloys. Recently, a new yield criterion proposed by Barlat has been incorporated into LS-DYNA3D to describe the anisotropic material behavior of aluminum alloys. This paper examines the influence of Von Mises', Hill's (1948) and Barlat's yield criteria on the FEM simulation results for the deep drawing of a square cup and cylindrical cup for aluminum alloys. The sensitivity of predicted results to yield criteria is examined for deformation behavior, strain localization and potential of wrinkling.

This paper presents the results of tests of one-piece face bars. It develops tentative guidelines for assessing the resistance of aluminum bumpers to local damage. Resistance to denting is shown to depend on the magnitude and location of the load applied, and the yield strength and thickness of the material. Cracking resistance is dependent on load applied, configuration of the bumper, location of load, tensile strength and thickness of the material. Deformation capacity of the material also appears to be of importance.

Two new aluminum alloys, 6009 and 6010, for auto body sheet are described and technical data are presented. The 6XXX-series alloys are ideal for body sheet in several respects, providing excellent corrosion resistance, improved spot weldability, and freedom from Luder's lines, together with favorable response to aging in many paint bake cycles. The result is a combination of excellent formability in the T4 temper and, after aging, higher strength than achievable in any other aluminum alloy system having other characteristics desired in body sheet. The latter translates to excellent dent resistance, superior even to that of steel. Furthermore, scrap loop problems are eliminated; compatible alloys 6009 and 6010 may be used together to obtain optimum strength and formability without any penalties in scrap utilization. Forming, aging, finishing, and joining data for these alloys are presented.

The use of polished aluminum fuselage skins has been a standard on U.S. commercial jet transport aircraft for decades. Increasingly stringent environmental regulations for paint stripping combined with fuel and maintenance savings allows consideration of flying polished non-painted aircraft. Boeing, McDonnell Douglas and Embraer currently manufacture commercial aircraft with polished alclad aluminum fuselages. Commercial airlines such as American Airlines, USAir, Eastern, Northwest and ASA fly non-painted fleets. These customers require the aircraft to be delivered with a polished appearance incorporating minimum fleet graphics. The manufacturing of polished aircraft requires unique production and handling procedures to fabricate all exterior panels with identical color match and reflectivity.