Effects of Deformation Processing on the Mechanical Properties of Aluminum Alloy 6063
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INTRODUCTION
AT room temperature, plastic deformation generally occurs in metals by dislocation motion. The stress required to move a dislocation depends on the characteristics of the atomic bonding and atomic arrangement (i.e., crystal structure), and on obstacles such as solute atoms, the presence and thickness of grain boundaries, and the precipitate particles introduced during casting. In fcc metals (e.g., Al and Cu), the effective stress is only weakly dependent on temperature. Thus, the dislocation motion remains high even at low temperatures and the material remains relatively ductile. Over the years, the deformation processing of materials has been of great importance since knowledge of the interrelationship among the process parameters, microstructure, and material properties will enhance the quality of the product. Deformation processing depends on the microstructure of the starting material, the geometry of the deformation zone, the temperature, the strain rate employed, and the frictional conditions.[1] The microstructure of the material being processed determines the extent of microstructural damage likely to be caused by mechanisms such as cavity formation at hard particles, cracking at grain-boundary triple junctions, and flow localization due to adiabatic cracking. Deformation forces increase with the flash width-tothickness ratio, and decrease with increasing billet diameter-to-height ratio and slug temperature, when forging EN3B mild steel slugs (composition in Table I) within the temperature range 1150 C to 1250 C.[2] This work studies the deformation processing of aluminum alloy 6063 with a view toward determining SANMBO A. BALOGUN, Professor, DAVID E. ESEZOBOR, Senior Lecturer, and SAMSON O. ADEOSUN, Lecturer, are with the Department of Metallurgical and Materials Engineering, University of Lagos, Akoka-Yaba, Lagos, Nigeria 23401. Contact e-mail: [email protected] Manuscript submitted August 8, 2006. Article published online June 26, 2007. 1570—VOLUME 38A, JULY 2007
the interrelationship among the process parameters, microstructure, and product properties. Matrix particles are known to influence cavity formation, while particles at the grain boundaries affect wedge cracking. In this study, upset forging and cold rolling of the material are evaluated, as are the longitudinal tensile properties produced by both processing routes.
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EXPERIMENTAL METHODOLOGY
A. Materials and Specimen Preparation Test specimens were prepared by melting an extruded scrap of 6063 aluminum alloy with about 98.45 pct Al and 0.45 pct Mg in an oil-fired crucible furnace. The alloy was cast into sand molds to obtain bars 140 · 25 · 16 mm in size. Table II gives the composition of the aluminum alloy evaluated in this study. The as-cast specimens were either rolled in five passes at ambient temperature (303 K) using a two-high mill or they were forged in a single pass at 303 K using a pneumatic hammer of 56.31 kPa and driven by a 4.5-HP electric motor. The initial specimen thickness was 16 mm. B. Mechanical Testing Figu
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