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

Abstract

The deformation behaviors below 0.2% offset yield stress in some silicon carbide particulate reinforced aluminum composites (SiCp/Al) and their unreinforced matrix alloys were investigated experimentally in this work. The results of the study showed that incorporation of SiC particulate into aluminum matrix can enhance the plastic flow stress (PFS) in macroplastic stage but slightly lower PFS in microplastic stage. With increase in the volume fraction of SiC particulate ( V p), the 0.2% offset yield stress ( σ 0.2) increases while the resistance to microplastic deformation ( σ 10 −5 ) first decreases and then increases. The composite with smaller particle size presents higher PFS both in micro- and macro-plastic stages. It was also found that heat treatment remarkably influence both micro- and macro-plastic behaviors of the composites. Quenching followed by artificial aging can significantly 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/2024Al composite and unreinforced 2024Al alloy, PFS exist a ‘peak value’ with variation of aging time, implying that like the conventional yield strength, 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 microplastic stage is very sensitive to the microstructure features. The lower residual thermal stresses, small density of moveable dislocations and harder matrix would be beneficial to the increase of PFS in microplastic stage in the composites.