1997 TMS Annual Meeting: Thursday Session

AUTOMOTIVE ALLOYS: Session III: Castings

Session Chairperson: Carl Seidler, Technical Service Manager, ARCO Aluminum, Inc., P.O. Box 32860, Louisville, KY 40232

8:30 am

A NEW CASTING DEFECT HEALING TECHNOLOGY: Edwin S. Hodge, Thomas W. Reddoch, Format Industries, Inc., Knoxville, TN; Srinath Viswanathan, Oak Ridge National Laboratory, Oak Ridge, TN

A new technology is presented for healing of defects in 356 and 201 Aluminum alloys that provides economic upgrading of these cast alloys. This technology uses pneumatic isostatic forging (PIF) to provide a unique capability to produce high quality Aluminum alloy products with enhanced mechanical properties that are uniform throughout the part thus permitting higher design allowables and increased usage of Aluminum alloy castings. The fundamental mechanism underlying PIF is a single mode plastic deformation process that uses isostatic application of pressures for 10 to 30 seconds at temperature. The process can be integrated in-line with other production operations, i.e., using the latent heat from the previous casting step. The results of applying the PIF process indicate lower cost and significant improvement in me chanical properties that rival and often exceed corresponding properties of other technologies like hot isostatic pressing (HIP) and related processes. This process offers many advantages that will be described in the paper in addition to presenting case histories of property enhancement by PIF, and the mechanism for responsible property enhancement.

9:00 am

TENSILE PROPERTIES OF 319 ALLOY CASTINGS: S. Viswanathan, W. Ren, Metals and Ceramics Division, Oak Ridge National Labs, Oak Ridge, TN 378316083, G.B. Ulrich, Y12 Plant, Oak Ridge, TN 378318096; M.E. Hoover, General Motors Powertrain Division, Saginaw, MI 486055073

Plate castings of 319 alloy were made over a wide range of thermal conditions by casting in sand molds, molds with end chills, and molds with top, bottom, and end chills. The plates were sectioned along their width into coupons. Odd-numbered coupons were machined into tensile specimens and tested in the as-cast condition. Even-numbered coupons were heat treated to a T6 condition, and then machined and tested. Yield strength, Ultimate tensile strength, and ductility measured by percent elongation were plotted with respect to distance from the chill end of the plate as well as related to porosity and other microstructural features such as dendrite cell spacing. The data shows that tensile elongation is a strong function of porosity. In particular, the data indicates a threshold value of porosity below which a sharp increase in ductility is observed. These effects as well as the effect of heat treatment and dendrite arm spacing are discussed. *Research sponsored by the U.S. Department of Energy Defense Programs, Assistant Secretary, Technology Management Group, Technology Transfer Initiative under contract DE-AC05-96OR22464 with Lockheed Martin Energy Research Corporation.

9:30 am

RECENT DEVELOPMENTS IN SQUEEZE CASTING OF MAGNESIUM ALLOYS AND THEIR COMPOSITES: Henry Hu, Alan Luo, Institute of Magnesium Technology (ITM, Inc., SteFoy, Quebec, Canada GIP 4N7

Squeeze casting, also known as liquid metal forging, extrusion casting and pressure crystallization, is a process in which molten metal solidifies in a die under an applied high pressure. The concept of squeeze casting was invented in Russia over 100 years ago. Later the process has been exploited in North America, Japan and Europe to produce various automotive components. With the rapid expansion of magnesium applications in the automotive industry, the development of squeeze casting technology for magnesium alloys and their composites has been motivated by incentive to produce high quality magnesium-based components. The present paper reviews recent progress in squeeze casting of magnesium alloys and magnesium-based composites. The effects of process variables on the cast structure and properties of magnesium alloys and magnesium-based composites are discussed. The significant advantages of squeeze cast magnesium alloys and magnesium-based composites are highlighted. The ongoing research work at ITM is presented.

10:00 am

CAST ALUMINUMFLY ASH COMPOSITES FOR ULTRALIGHT AUTOMOTIVE APPLICATION: P.K. Rohatgi, R.Q. GUO, Department of Materials, University of Wisconsin, Milwaukee, WI 53211

Coal fly ash, an industrial waste by-product, is produced during combustion of coal by thermal power plants. Additions of solid or hollow particles of fly ash into aluminum melt by common foundry techniques reduce the cost and density of aluminum castings while increasing their performance. Fly ash particles are very light materials with density around 2.1 to 2.3 g/cm3 for solid fly ash particles and a density as low as 0.4 to 0.8 g/cm3 for the cenospheres of fly ash which are hollow. In this paper, manufacture and some properties of aluminum-fly ash composites (Ashalloy) have been studied. Aluminum alloy-fly ash (Ashalloy) represents a candidate ultralight material for automotive application. Incorporation of cenosphere fly ash particles, which are hollow with very low density, significantly reduces the density of material. Some of the characteristics of fly ash used for making composite have been described. The fly ash particle shape, size, and density have been determined. Mechanical properties of aluminum alloy - fly ash composites made by stir casting show that the composites have similar hardness, elastic modulus as matrix aluminum alloy, and improved wear abrasive resistance compared to the matrix alloy. Several prototype components of aluminum - fly ash composites for automotive applications, small engine and electromechanical machinery have been made and are under trials.

10:30 am BREAK

11:00 am

EFFECT OF SECTION THICKNESS AND GATE VELOCITY ON EVOLVED MICROSTRUCTURE AND MECHANICAL PROPERTIES OF HIGH PRESSURE DIE CAST MAGNESIUM ALLOY AZ91D: Winston P. Sequeira, Gordon L. Dunlop, CRC for Alloy and Solidification Technology (CAST), The University of Queenland, St. Lucia, Qld 4072, Australia, Morris T. Murray, CSIRO Division of Manufacturing Technology, Preston, Vic 3072, Australia

This paper investigates the change that occurs in microstructure and mechanical properties when the section thickness is varied for high pressure die cast Mg alloy AZ9lD. It has been found that yield and ultimate tensile strength increase more than would be expected with decreasing section thickness. This is explained in light of the fine microstructure in the surface layer (skin) that develops during the rapid solidification that occurs in this process. The two stage solidification sequence which leads to the evolution of the unique microstructure in die castings has been supported by evidence from solidification experiments using wedge castings and computer simulation of the shot sleeve. Two different die castings with relatively thick cross sections have been compared in terms of their porosity content and its effect on mechanical properties. Finally, the effects on mechanical properties of thick and thin specimens due to variation of casting parameters such as gate size is also discussed.

11:30 am

DUCTILE PRESSURE DIE CASTING FOR AUTOMOTIVE APPLICATIONS--A Status Report: Hubert Koch, Alois J. Franke, Aluminum Rheinfelden, GmbH, P.O. Box 1140, D79601 Rheinfelden, Germany

After three years of commercial application of low iron pressure die casting alloys for structural parts, this paper reviews industrial scale experience and looks out to further potential in alloy development. Silafront-36TM (AA 365) and Magsimal-59TM both have an iron content below 0.13 wt% ensuring good ductility of the casting while completely avoiding soldering or sticking to the die in manufacturing. This is a breakthrough in pressure die casting where during decades the soldering problem has prevented the application of ductile casting alloys. Silafront-36TM (AA 365) and Magsimal-59TM are used for suspension parts, steering wheels, space frame nodes, motor mounts etc. High pressure die casting and squeeze-casting are the processes applied. Silafront-36TM is an AlSi9Mg-type alloy that can be heat treated and welded. Magsimal-59TM is of the AlMgMnSi-type and specially designed for applications without heat treatment with extraordinary mechanical and dynamic properties. This paper describes the manufacture of the castings, the application and component properties for both alloys.