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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.

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.

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.

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.

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.

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

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.

Dynamic denting tests have been conducted on actual autobody components and on simulated panels fabricated from aluminum and steel sheet at impact velocities of 20 to 125 mph. These experiments give additional evidence that dent depth is a linear function of impact velocity. They also show that autobody components fabricated from aluminum sheet can have equal or improved dent resistance compared to the same components fabricated from the steel alloys currently used. Primary factors to be considered in comparing dynamic dent resistance are sheet thickness, yield strength, modulus of elasticity, density and geometric shape.

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.