1. Journée des étudiants du REGAL 27 octobre 2004 Effect of Metallurgical Parameters on the Machinability of 356 and 319 Casting Alloys. M. TASH 1,2, F. H. Samuel 1, F. Mucciarrdi 3, H.W. Doty, 4 1 Université du Québec a Chicoutimi, Chicoutimi, Québec, Canada 2 Cairo University, Giza, Egypt 3 McGill University, Montreal, Québec, Canada 4 General Motors Powertrain Group, Metal Casting Technology, USA In this work, Al-Si-Cu, Al-Si-Cu-Mg and Al-Si-Mg cast alloys, belonging to the Al-Si alloy system and represented respectively by 319 and 356 alloys, were selected for machinability study, due to the high demand of these alloys in the automobile industry. A thorough understanding of all of the metallurgical factors affecting their machinability will help in selecting metallurgical adjustment trying to achieve the optimum machining performance at high speed machining. In a collective sense, the most important terms as related to the subject of machinability are; tool wear, chip formation, burring tendency and finish of machined surface. The most important factors that can influence the outcome of the machinability are: Alloy chemistry, additions, Morphology, size and volume fraction of the constituent phases, Microstructure (grain refining and modification), Porosity, Heat treatment and mechanical properties. Copper and Mg decreases the tendency of an alloy to build up on a cutting tool edge. [1,2] Heavy elements (Mn and Cr) tend to combine with Al, Fe, Si, and sometimes Cu to form hard complex intermetallics phases (sludge or fall-out) that cause hard spots and cause build-up problems and tool breakage. Modification of intermetallics by the addition of Mn/Fe up to 0.5 to convert the β- Fe needles into the more compact and less harmful α-Fe script phase particles. A fine, well-modified eutectic silicon structure is far less detrimental to tool life than heavy-element intermetallics impurity phases. [1] Tool life suffers by more rates with the coarse eutectic silicon structure. [1] Heat build-up on the cutting tools is the biggest drawback for maintaining a material machining characteristics. Most automotive machine shops agree that a minimum hardness of 80 Brinell to avoid difficulties associated with Heat built-up-edge (BUE) on the cutting tool. [1] Any metallurgical adjustment that can be made to such alloys which allows them to enhance the effectiveness of the coolant or reduce the amount of heat generated can be considered an improvement in the overall machinability. OBJECTIVES I. Metallurgical characterization of 356 and 319 alloys (hardness and microstructure) 356 base alloy (Al- 6.55% Si-0.28%Mg-0.11%Fe-0.03%Cu) 319 base alloy (Al- 5.99% Si-3.45%Cu-0.23%Fe-0.01%Mg) Different additions of Fe and Mn for both alloys in the unmodified and Sr- modified conditions were made to obtain different volume fractions and morphologies of Fe-intermetallics. Copper and Fe-intermetallic volume fraction were measured in the as-cast and solution heat-treated conditions for different alloy compositions (44 conditions) All the alloys were grain refined using Al-5Ti-1B master alloy. Heat treatment of both 356 and 319 (with and without Mg additions) alloys were carried out to get similar two level of hardness for both alloys. II.Machinability study of 356 (0.4%Fe + 0.3%Mn) and 319 (0.4%Fe + 0.3%Mn + 0.1 and 0.3%Mg and 1%Fe + 0.4%Mn + 0.1 and 0.3%Mg) alloys; through the role of Copper and Mg, α-Fe-intermetallics volume fraction, and Heat treatment temper (T6 and T7) on machining performance of 356 and 319 alloys (drilling and tapping at fixed machining conditions). Summary [1][1] J. Jorstad, “Influence of Aluminum Casting Alloy Metallurgical Factors on Machinability,” Society of Automotive Engineers, 400 Commonwealth Dr., Warrendale, pa.15096., 1980 (Report, 15 pages) [1] [2] J. Jorstad, “Machinability of 380 Alloy : Effect of Minor Elements and Impurities”, Paper #G-T79-072, Transactions of the Society of Die Casting Engineers, 1979. Robert C. Lemon, “Metallurgical Factors Related to Machining Aluminum Castings,” Paper# 607465 presented at SAE Congress and Exposition, January 1967. [3] Robert C. Lemon, “Metallurgical Factors Related to Machining Aluminum Castings,” Paper# 607465 presented at SAE Congress and Exposition, January 1967. [3] Force a Microstructural constituents: Sludge particles α-Fe Script particles β-Fe platelet CuAl2 intermetallic type particles Well modified eutectic Si Shrinkage Porosity β -Fe Sludge porosity α- Fe Mg 2 Si 319 alloy chip formation build-up problems