1997 TMS Annual Meeting: Wednesday Session

AUTOMOTIVE ALLOYS: Session II: Process/Product Applications

Session Chairperson: Dr. George J. Kipouros, Technical University of Nova Scotia, Department of Mining, and Metallurgical Engineering, P.O. Box 1000, Halifax, Nova Scotia, Canada B3J2X4

2:00 pm

FILLER METAL-ASSISTED RESISTANCE SPOT WELDING TECHNIQUE: Hua-Xin Li, Mark T. Smith, Pacific Northwest National Laboratory, P.O. Box 999, Richland, WA 99352

A new technique is developed to overcome or minimize the inherent problems associated with aluminum RSW. Test results on 1 mm thick 6061 aluminum alloy sheets have shown that the new method can dramatically improve almost all of the problems encountered using conventional RSW. By using the new method, the following improvements have been achieved: 1) reducing/eliminating electrode contamination; 2) eliminating/minimizing surface indentation and deformation; 3) increased weld nugget size by 200% with same welding parameters; 4) maintaining consistent weld nugget size; and 5) no cleaning is needed, particularly at faying surfaces. Peeling strength is high and failure in peeling testing occurs in base metal around weld nugget. Metallographic investigation shows favorable oval nugget shape on cross section, which can improve weld nugget high peeling strength. The ratio of major axis to minor axis is 7 with major axis being 6.5 mm long. Weld nugget mechanical properties such as tension-shear strength is being evaluated and will be presented.

2:30 pm

INFLUENCE OF MICROSTRUCTURE AND THERMAL HISTORY ON THE CORROSION SUSCEPTIBILITY OF AA5083: J.S. Vetrano, R.E. Williford, S.M. Buremmer, R.H. Jones, Pacific Northwest National Laboratory, P.O. Box 999, Richland, WA 99352

The utilization of aluminum alloys for lightweight automotive structures can be increased by improved formability and a reduction of stress corrosion cracking (SCC) problems associated with magnesium additions greater than about 3%. We have utilized a series of thermomechanical treatments on several 5xxx alloys (5052, 5082, 5083, 5454 and 5754) to alter the dispersoid density and size, as well as the distribution of eutectic constituents. The aim has been to optimize grain size for specific forming operations and post-formed properties. In addition, the role of the grain size and particle distribution, as well as the magnesium content and microstructure, on the SCC resistance has been investigated. It was found that the grain size could be controlled by the distribution of the dispersoid particles, with a minimum grain diameter of 8 µm achieved in the 5083. The effect of grain size on SCC susceptibility was also evaluated.

3:00 pm

APPLICATION OF THE METAL COMPRESSION FORMING PROCESS FOR THE PRODUCTION OF AN ALUMINUM ALLOY COMPONENT: R.M. Purgert, Precision Metal Forming Co., P.O. Box 25441, Garfield Heights, OH 44125; S. Viswanathan, Metals and Ceramics Division, Oak Ridge National Lab, Oak Ridge, TN 37831-6083

Metal Compression Forming (MCF) is a variant of the squeeze casting process, in which molten metal is allowed to solidify under pressure in order to close porosity and form a sound part. However, the MCF process applies pressure porosity and form a sound part. However, the MCF process applies pressure on the entire mold face, thereby directing pressure on all regions of the casting and producing a uniformly sound part. The process also enhances the solidification rate of the metal promoting a very fine grain structure which results in improved properties. Consequently, the process is capable of producing parts with properties close to that of forgings, while retaining the near net shape, complexity in geometry, and relatively low cost of the casting process. The paper will describe the casting process development involved in the production of a 356 alloy engine mounting bracket, including the use of a filling and solidification model to design the gating and determine process parameters. Tensile and fatigue properties of the component will also be presented and correlated with those of forged components. *Research sponsored by the U.S. Department of Energy under contract DE-AC05-96ORT22464 with Lockheed Martin Energy Research Corporation.

3:30 pm BREAK

4:00 pm

MICROSTRUCTURAL AND TRIBOLOGICAL PROPERTIES EVALUATION OF CHAR-REINFORCED Al-Si ALLOY COMPOSITES: J.U. Ejiofor, R.G. Reddy, Department of Metallurgical and Materials Engineering, The University of Alabama, P.O. Box 870202, Tuscaloosa, AL 35487

The application of carbon-reinforced aluminum composites in electromechanics has continued to attract new research investigations. The factors of interest range from low cost and availability of materials to low-temperature processing methods. This study has investigated the conventional double-compaction, powder metallurgy processing of Al-13.5Si-2.5Mg alloy (wt.%) reinforced with coconut shell chars. The mechanical, physical and relevant tribological properties were determined after achieving the optimum compaction and sintering conditions. Use of optical microscopy, EPMA, SEM and energy dispersive analysis were made in characterising the matrix-reinforcement interfaces, the fracture surfaces and the nature of the adhesive dry wear. At 0.02Vf of the char, the alloy exhibited properties suitable for antifriction applications. Increased additions of the chars resulted in largely reduced strength, hardness and sintered density. This is attributed to poor bonding of the char particles with the matrix alloy. Parallel investigations with palm-kernel shell char as the filler phase yielded identical results. Initial formation of A14C3 in the composites was detected at a sintering temperature of 600°C. Reinforcement of the alloy with chars activated in CO2 to various bum-off percentages were found to yield marginal results.

4:30 pm

ADVANTAGES OF CERAMIC COMPONENTS IN THE LOW PRESSURE CASTING PROCESS FOR ALUMINUM WHEELS: J. Pennemann

Abstract not available.