An experimental study on deformation behavior below 0.2% offset yield stress in some SiCp/Al composites and their unreinforced matrix alloys

The deformation behaviors below 0.2% offset yield stress in some silicon ca rbide particulate reinforced aluminum composites (SiCp/Al) and their unrein forced matrix alloys were investigated experimentally in this work. The res ults of the study showed that incorporation of SIC particulate into aluminu m matrix can enhance the plastic flow stress (PFS) in macroplastic stage bu t slightly lower PFS in microplastic stage. With increase in the volume fra ction of SiC particulate (V-p) the 0.2% offset yield stress (sigma (0.2)) i ncreases while the resistance to microplastic deformation (sigma (10-5)) fi rst decreases and then increases. The composite with smaller particle size presents higher PFS both in micro- and macro-plastic stages. It was also fo und that heat treatment remarkably influence both micro- and macro-plastic behaviors of the composites. Quenching followed by artificial aging can sig nificantly enhance PFS both in micro- and macro-plastic stages for the age hardened alloy based composites (SiCp/2024Al) but has no obvious effect for the non-age hardened alloy based composites (SiCp/Al). For both the SiCp/2 024Al composite and unreinforced 2024Al alloy. PFS exist a 'peak value' wit h variation of aging time, implying that like the conventional yield streng th, PFS in microplastic stage of the composite is also strongly controlled by the precipitates formed in matrix during aging treatment. The effects of thermal cycling on PFS are dependent to the V-p. In large V-p case (35%), with increase in cyclic number PFS slightly decreases but in small V-p case (15%) PFS slightly increases as the cyclic number increases. The PFS in mi croplastic stage is very sensitive to the microstructure features. The lowe r residual thermal stresses, small density of moveable dislocations and har der matrix would be beneficial to the increase of PFS in microplastic stage in the composites. (C) 2001 Elsevier Science B.V. All rights reserved.