Fatigue Performance of Fluidized Bed Heat Treated 319 Alloy Diesel Cylinder Heads
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AL-SI-MG-CU alloys (such as 319 series) are widely used for many automotive components due to their castability characteristics and good mechanical properties.[1,2] Since the use of these alloys is experiencing tremendous growth, there is the need to evaluate the fatigue performance of actual components rather than small coupons cast in the laboratory. Studies on fatigue behavior of alloys are important because it is the cause of failure in 80 pct of structural materials resulting in huge monetary losses. Therefore, the need to enhance the fatigue life of materials is of paramount value to automotive and aerospace industries. Fatigue properties of cast Al components strongly depend on casting SUJOY K. CHAUDHURY, Lecturer, is with the Metal Processing Institute (MPI), Worcester Polytechnic Institute (WPI), 100 Institute Road, Worcester, MA 01609, and also with the Department of Metallurgy, Indus University, Ahmedabad, India. DIRAN APELIAN, Alcoa-Howmet Professor of Engineering, is with the Metal Processing Institute (MPI), Worcester Polytechnic Institute (WPI). Contact e-mail: [email protected] PHILIPPE MEYER, VP & CTO of Aleris, is with the Montupet S.A, 67 rue Jean de la Fontaine, 60180 Nogent Sur Oise, France and also with the Aleris, 56070, Koblenz, Germany. DENIS MASSINON, Director Innovation and Process Engineering, and JULIEN MORICHON, Project Engineer, are with the Montupet S.A, 67 rue Jean de la Fontaine, 60180 Nogent Sur Oise, France. Manuscript submitted August 20, 2007. METALLURGICAL AND MATERIALS TRANSACTIONS A
defects.[3,4] There exists a difference in opinion as to which microstructural characteristic plays a dominant role on fatigue properties; for example, some experimental data support the view that refining the dendritic arm spacing (DAS) and the size of eutectic Si particles improve fatigue strength[5]; while others[6] have reported that DAS has no effect on fatigue strength in 319 alloy. However, there is no ambiguity that casting defects always have deleterious effect on fatigue strength.[7–11] Liquid Al is prone to hydrogen adsorption and oxidation. Consequently gas porosity and oxide inclusions are inevitably found in cast alloys. In addition, shrinkage porosity due to improper feeding can also reduce the fatigue strength of alloys. Fatigue properties of Al alloys depend on several factors. Among them, solidification time and heat treatment play a vital role. It has been reported that fatigue strength decreases with the increase in solidification time when the casting was treated to T6 temper (i.e., solutionized, quenched, and peak aged).[12] On contrary, when the casting was treated to T7 temper (i.e., solutionized, quenched, and over aged), the fatigue strength decreases with decreasing solidification time. Grain size varies inversely with solidification time. However, in castings containing porosity, heat treatment had no noticeable effect on fatigue strength.[12] Chan et al. studied the effect of heat treatment on fatigue crack growth and fracture paths in sand cast
B319 alloy.[13] They repor
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