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Aluminum use for automotive body sheet applications is growing. This growth requires improvement of related joining processes and technology. Resistance spot welding will be one of the major joining technologies used in assembling automobiles. When spot welding aluminum, electrode tip life is limited by tip erosion and pickup of aluminum on the tip. Increasing weld current improves weld strength (to a limit), however this reduces tip life. This study examines the control variables in the resistance spot welding process and offers an improved weld schedule to achieve desired weld properties while maximizing tip life. First, the limits of weld parameters where satisfactory welds can be obtained are determined. A window of tip force and weld current is established for a given material and tip geometry. These limits are used to optimize the weld schedule in terms of tip life. Spot welds fail on the basis of shear strength, button diameter or peel rate.

The use of aluminum in automotive applications is growing. The 1991 calendar year automobiles used over 190 pounds per vehicle. The growth for aluminum applications is expected to be significant over the next ten years. Expected changes in end use and alloy mix pose challenges to the recycling system. These challenges need consideration by both the automotive and aluminum industries. This paper discusses these challenges and presents detailed analysis of the weight and chemistry aspects of automotive aluminum recycling. It also demonstrates a feasible and efficient recycling system in which post-consumer scrap is consumed in new production.

The aluminum alloy 2036 is presently being used in the production of automotive body panels. In the study presented, specimens of 2036-T4 with varying crystallographic textures were subjected to tensile testing and limiting dome height (LDH) evaluations in an effort to gauge the effect of texture on formability and stamping performance. To describe the texture, relative magnitudes of ideal texture components were derived from the orientation distribution function. Finite element analysis was used to study the effect of anisotropic properties due to texture on thinning in the LDH test. The impact of textural character on formability is discussed.

An evolutionary state variable model is used to predict failure in sheet forming. The development of damage in aluminum sheet is characterized using Bammann's plasticity model. Simulations are carried out with the commercial code LS-Dyna3D. Using the limiting dome height test as an example, the prediction of failure in straining states of draw, plane strain, and stretch is made for AA 6111-T4 sheet. The location of failure and associated major/minor strains are contrasted with experimental forming limit curves. As a further example, the drawing of a square cup from a 5000 series alloy blank is simulated and compared with experimental data. The simulations accurately predict the location of failure and show limit strains which compare favorably with experiment. The damage variable provides a method for predicting the location and time of failure in a framework that accommodates general straining paths.

A new electrode holder designed for resistance spot welding of aluminum twists the electrode while it contacts the workpiece. The limited rotation grinds the electrode tip into the surface of the workpiece, abrading it and obtaining good electrical contact. The improved electrical contact results in less heat generation at the tip/workpiece interface, which leads to longer tip life and more consistent welds. Test results show that tip life increases nearly 500 percent when using a twisting electrode holder. In addition, weld quality is improved and more consistent welds are produced than with standard spot welding practice. By using these new electrode holders, automobile manufacturers will decrease the downtime associated with replacing electrode tips and reduce the number of assemblies that have to be torn apart for quality control inspection.

Tailored blanks have been produced by a variety of welding processes. Currently, laser welding and mash seam welding are commonly used to produce steel blanks for automotive stampings. Because of the high electrical and thermal conductivity of aluminum, mash seam welding is generally not suitable for this application. Laser welding is currently in the developmental stage for welding aluminum. Reynolds Metals Company is investigating another existing welding technology -- Gas Tungsten Arc Welding (GTAW)--for welding of aluminum tailored blanks. Using the GTAW process, production weld speeds approximating those of laser systems can be obtained. Additionally, good control of weld geometry and quality can be easily attained. This study focuses on GTA welding process parameters for joining various alloys, tempers, and thickness of aluminum. Additionally, performance of welded joints in terms of strength, ductility, and formability are discussed.

The history of the development of sheet aluminum wheels, including alloy selection, properties, and tests are discussed. A number of alloys were considered for wheel application. The strain hardening characteristics, the excellent corrosion resistance and other property criteria led to the selection of 5454 as the sheet aluminum wheel alloy

This paper discusses the technique and problems associated with in-plant and body shop repair of aluminum auto body sheet. Metallic and nonmetallic repair procedures are discussed for in-plant repair of aluminum auto body sheet. An after-market procedure for repair of aluminum sheet is also presented, as well as a new procedure for arc welding of thin gauge aluminum sheet for in-plant and after-market repair.

The dent resistance of aluminum and steel autobody panels has been studied under controlled laboratory conditions and by field observations and measurements of actual hailstone damage. Analysis of the results shows that very nearly the same response occurred in the lighter weight aluminum components as occurred in the steel panels. The autobody components were all 1977 model year production panels. Laboratory testing included four steel and four aluminum hoods, both painted and unpainted. The hailstone damaged components included a steel hood, aluminum doors and an aluminum fender. The aluminum and steel panels were damaged in the same hailstorm during May 1977. The analysis of denting resistance presented in this paper is based on insight and experience gained from a four-year cooperative program of Reynolds Research and several automobile companies.

High integrity aluminum castings are potential replacements for cast iron in current vehicle weight reduction programs. Domestically, several cast aluminum structural-type components are already realities, saving weight and contributing to improved fuel economy; wheels, brake drums, master brake cylinders and power steering housings. In Europe, suspension components, wheel hubs and disc brake calipers are cast in aluminum for some car models, indicating the functional and economic feasibility of such parts. Alloy and process technology already exist to enable production of realiable, high strength aluminum castings. Domestic automotive product engineers are urged to carefully consider and thoroughly test such aluminum castings along with the many other weight reduction possibilities currently being investigated.

A discussion of aluminum bumper systems, alloy data fabrication performance, and costs are presented. Weights and costs of similar steel, aluminum, and urethane face systems are compared and the effect of weight savings on costs and fuel economy is determined. Areas for product improvements are explored.

The Reynolds’ 390 engine technology eliminates the need for iron bore liners in aluminum engines. This allows casting of the cylinder block and bores as an integral unit. The technology is a three-part system consisting of the hypereutectic 390 aluminum-silicon alloy, compatible pistons and a special cylinder bore finish. When properly applied, it can produce a lightweight, strong, compact and relatively low-cost aluminum engine block.

A discussion of the impact of a 2.5 mph bumper standard on aluminum sheet and extruded bumpers is presented. Information is presented on energy management systems, bumper shape, and dentability. This information can be used to determine whether a sheet or extruded bumper is the most efficient for a particular application.

Recent trends in the automotive industry toward improving fuel economy have led to the conversion of many steel applications to aluminum. The use of aluminum reduces vehicle weight while allowing the automaker to continue to use traditional fabricating methods. The primary joining technique used for steel sheet components has been resistance spot welding. While this technique is currently used to join many aluminum components, automakers are reluctant to specify this joining technique due to capital equipment cost, electrode tip life, or reliability concerns. Several alternate joining techniques have been investigated and used. These include adhesive bonding, weld bonding, resistance welding with arc cleaning (1, 2)*, GMA spot welding, clinching, and riveting. Recently, a method of riveting components without prepunching or pre-drilling holes has generated a large amount of interest. This paper is a review of this riveting technique.

One joining technique that is receiving increased attention is mechanical fastening with a steel self-piercing rivet. The use of steel rivets in direct contact with aluminum components raises questions concerning galvanic corrosion. To determine if a corrosion problem exists, aluminum samples were joined by two processes--resistance spot welding and steel self-piercing rivets. Replicate samples using two aluminum alloys were tested for 90 days by alternate immersion in 3.5% NaCl water solution. After alternate immersion exposure, the integrity of the joint was evaluated by shear testing. Joint shear strengths and the metallographic corrosion evaluations are presented in this paper.

A new type plated electrode has been developed which shows considerable promise for spot welding mill finish and mechanically cleaned aluminum sheet. This electrode consists of preconditioning the tips of regular Class I and Class II electrodes followed by an inexpensive electroplating of dull nickel. Laboratory data has shown that 2000 spots can be made on mill finished 2036 aluminum using this plated electrode. On wirebrushed 5182-0, 3750 welds were made before failure occurred. This represents a significant increase in tip life compared to tests run using regular copper electrodes. The paper gives details as to how the nickel plated electrodes were developed. This includes results from evaluating other electrode plating and capping materials. The results of tests run using the plated electrodes are included as part of the paper, as well as a discussion as to why the nickel plating works when spot welding aluminum.

Dynamic denting properties of aluminum and steel autobody panels have been experimentally measured under controlled conditions. Material, geometric and dynamic factors have been graphically and statistically evaluated to determine design equations. For impact velocities of 20-60 mph and sheet gauges of 0.027-0.040″, dent depths are shown as linear functions of impact velocity. This linear velocity model incorporates sheet thickness, yield strength, density and modulus of elasticity of the alloy used, as well as the geometric shape of the fabricated panel. As an example, for equal dent resistance, a panel of 2036-T4 aluminum would need to be 10-13% thicker than the same panel fabricated from 0.035″ gauge 1010-CQ steel.

Aluminum castings have much to offer the automotive industry in terms of weight reduction and energy savings. Their long-term acceptability can only be assured, however, by applying the most cost-effective combinations of material and processing. This paper will point out some “cost-saving” opportunities in two basic areas: (1) The use of hypereutectic aluminum-silicon alloys to eliminate a need for ferrous wear-surface inserts, to reduce machining capital expenditures and to reduce overall part weight; and (2) The use of two processing methods, “Pore-Free” die casting and “low-pressure” casting, to produce aluminum parts with minimum metal usage and energy consumption.

Tailor welded blanks are finding increasing application in automotive structures as a powerful method to reduce weight through material minimization. As consumer demand and regulatory pressure direct the automotive industry toward improved fuel efficiency and reduced emissions, aluminum alloys are also becoming an attractive automotive structural material with their potential ability to reduce vehicle weight. The combination of aluminum and tailor welded blanks thus appears attractive as a method to further minimize vehicle weight. Two major concerns regarding the application of aluminum tailor welded blanks are the formability and durability of the weld materials. The current work experimentally and numerically investigates aluminum tailor welded blanks ductility, and experimentally investigates their fatigue resistance.