HIGH-TEMPERATURE MECHANICAL AND MICROSTRUCTURAL BEHAVIOR OF A356 15 VOL-PERCENT SICP AND A356 ALLOY/

A metal-matrix composite (MMC, 15 vol% SiCp/A356 Al) and its matrix al loy were subjected to hot torsion over the range 300-540 degrees C and 0.1-5.0 s(-1). Flow stresses of the A356 MMC were found to be much hi gher than A356 alloy at low temperatures but the difference was quite small at higher temperatures. Flow stresses were found to depend on th e strain rate through a sinh function and on temperature through an Ar rhenius term with activation energies of 263 kJ/mol for the composite and 161 kJ/mol for the matrix; the increased value for the composite s uggests that the SiC particles cause the matrix to undergo additional strain hardening. The substructures in both materials increase in cell size and decrease in internal and wall density, as temperature T rise s and strain rate (epsilon) over dot falls; the composite shows much g reater and less uniform dislocation density to which the strengths of the two materials are related. Dynamic recovery seems to be predominan t in A356; however, dynamic recrystallization likely nucleates in the vicinity of silicon carbide particles in 15 vol% SiCp/A356 Al. Ductili ty of the composite, about 25% below that of the alloy, rose by a fact or of 4 between 400 and 500 degrees C to become higher than many wroug ht alloy composites. The low ductility of A356 was shown to result fro m linking up of the cracks nucleated at coarse Si particles, whereas l inkage of the decohesion voids at the SiC was associated with more pla stic flow in the matrix which had much finer Si particles than the bul k alloy. (C) 1998 Canadian Institute of Mining and Metallurgy. Publish ed by Elsevier Science Ltd. All rights reserved.