Creep Properties of the As-Cast Al-A319 Alloy: T4 and T7 Heat Treatment Effects
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CAST Al-Si-Cu-Mg alloys are characterized by a high strength/density ratio, good corrosion and wear resistance, as well as elevated fatigue strength.[1,2] They are also known as the automotive A319 alloys and they are widely employed for casting fuel efficient engine blocks.[3] Numerous works have been published on the tensile and fatigue properties of Al-Si-Cu-Mg alloys, as well as on their respective microstructural features.[4–10] In particular, the deformation behavior of the Al-Si, Al-Si-Cu, and Al-Mg-Si alloys has been extensively investigated.[11] However, most of these works have been carried out at room temperature and there is limited information related to the creep properties of Al-SiCu-Mg alloys,[12–16] particularly for A319 Al alloys in the as-cast condition.[12] In the case of A319 Al alloys, they are cyclically exposed to relatively high temperatures for extended periods of time in the engine bore sections where internal combustion occurs. In turn, it is HAMID R. ERFANIAN-NAZIFTOOSI, Ph.D. Candidate, and HUGO F. LO´PEZ, Professor, are with the Department of Materials Science and Engineering, University of Wisconsin-Milwaukee, Milwaukee WI 53201. Contact e-mail: [email protected] ERNESTO J. RINCO´N, Research Professor, Graduate Coordinator, is with the Environmental and Mechatronics Engineering Department, Instituto Tecnolœgico de Nuevo Leon Ave. Eloy Cavazos, 2001, Col. Guadalupe, NL 67170, Me´xico. Manuscript submitted October 30, 2015. Article published online May 18, 2016 4258—VOLUME 47A, AUGUST 2016
desirable to experimentally establish the alloy response to high-temperature deformation behavior, particularly the creep response. Most published works on creep behavior have been confined to pure aluminum, wrought Al alloys, and aluminum solid solutions.[17,18] According to the published literature, it is found that in pure Al or in Al solid solutions class I the power law exponent, n, is either 3 or 5 with the value of 3 corresponding to dislocation viscous glide and n = 5 to the climbing of lattice dislocations.[19–21] In class II alloys, n is typically 5 and it is associated with dislocation climb control.[22] In all of these cases, the reported apparent activation energies Qa are close to those for Al self-diffusion (QD = 143 kJ/mol[17]). Moreover, n exponents of up to 8 have been reported, which have been attributed to the development of a constant subgrain structure in Al and Al-dispersion-strengthened alloys.[23] Al A319 alloys do not belong to either class I or class II alloys. These alloys exhibit the classic ‘‘Chinese scripture’’ and contain numerous Fe-, Cu-, Mg-, and Si-based coarse intermetallic phases including the Al2Cu and MgSi eutectics.[24] The mechanical properties of Al A-319 alloys can be modified through solid solution and aging treatments to achieve a distribution of coherent and incoherent precipitates within the matrix.[21] In addition, this alloy contains a distribution of rather coarse intermetallic phases. In particular, the presence of second phases
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