Effect of cold-rolling on hardness of SiC_w/Al composite

Abstract

A SiC_w/Al composite was fabricated through a squeeze cast route and cold rolled to about 30%, 50% and 70% reduction in thickness, respectively. The length of whiskers in the composite before and after rolling was examined using SEM. Some of the rolled composites were annealed by recrystallizing to remove the work hardening of the matrix alloy. The hardness of the rolled and annealed SiC_w/Al composites was examined and then associated with the change of the whisker length and the work hardening of the matrix alloy. It was found that the hardness was a function of the degree of cold rolling. For the cold rolled composites, with the increase in the degree of cold rolling, the hardness increases at furst, and decreases when the degree of cold rolling exceeds 50%. For the annealed ones, however, the hardness decreases monotonously with the increase in rolling degree. The different changes in hardness between the rolled and annealed composites could be attributed to a result of the competition between the work hardening of the matrix resulting from the cold rolling and the work softening arising from the change of whisker length.

Keywords

metal matrix composites / cold rolling / hardness / microstructure

References

[1] Nair S V. SiC Reinforced Aluminium Metal Matrix Composites. International Materials Reviews, 1985, 30(6): 275-295.

[2] Wang W M, Fu Z Y, Wang H. Combustion Synthesis and Densification of NiAl/TiB₂ Composites. J. Wuhan University of Technology—Mater. Sci. Ed., 2002, 1(1): 1-5.

[3] Humphreys F J, Miller W S, Djazeb M R.. Microstructural Development during Thermomechanical Processing of Particulate Metal-matrix Composites. Mater. Sci. Tech., 1990, 6(11): 1157-1166.

[4] Suganuma K, Okamoto T, Suzuki N. Semisolid Extrusion of Aluminium Alloys Reinforced with Alumina Short-fibre Cladding. J. Mater. Sci. Lett., 1987, 6(11): 1347-1348.

[5] Suganuma K, Fujita T, Niihara T. Hot Extrusion of AA7178 Reinforced with Alumina Short Fibre. Mater. Sci. Tech., 1989, 5(3): 249-254.

[6] Rack H J, Niskanen P W. Extrusion of Discontinuous Metal Matrix Composites. Light Metal Age, 1984, 2(1): 9-12.

[7] Lieblich M, Gonzalez-doncel G, Adeva P. Extrudability of PM 2124/SiCp Aluminium Matrix Composite. J. Mater. Lett., 1997, 16(19): 726-728.

[8] Zhang W L, Cai L C. The Forming Process of Hot-extruded SiC_w/6061Al Composites. Trans. Nonferrous Met. Soc. China, 1998, 8(3): 432-436.

[9] Zu L L, Luo S J. Study on the Powder Mixing and Semi-solid Extrusion Forming Process of SiCp/2024Al Composites. Journal of Materials Processing Technology, 2001, 114(3): 189-193.

[10] Zhang W L. High Strain Deformation and Recrystallization of SiC_w/Al Composites, 1999 Harbin: Harbin Institute of Technology. 67-67.