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The present work studies the microstructure and corrosion behaviour of 25 vol.% SiCp/AA2124-T4 metal matrix composites (MMCs) and AA2124-T4 aluminium alloy; and also the capability of excimer laser surface melting (LSM) to improve the corrosion resistance of the SiCp/AA2124 MMC and the monolithic alloy (MA). Microstructural characterization has shown significant influence of the presence and size of SiC particles on the fine Al2Cu precipitate and Mg segregation at SiC/Al interfacial regions. Such precipitates are revealed to be active sites for corrosion initiation in the MMCs, while the preferential sites for corrosion initiation in the MA are the coarse intermetallics. Corrosion evaluation performed in a 0.6 M NaCl solution suggests that the corrosion resistance of the MMC reinforced with micrometre-sized SiC particles is inferior to that of the MA and the MMC reinforced with submicrometre-sized SiC particles. The submicrometre-sized SiC particles have little adverse effect on the corrosion resistance of the MMC due to the reduced interfacial precipitates. Thin films of up to several micrometres have been achieved by excimer LSM on both the MMC and the MA. The surface roughness and the thickness of the melted layer increase with increasing laser fluence. High number of pulses (40 P) results in significant porosity in the MA and networks of cracking in the MMC. A homogeneous layer without chemical segregation except the Cu-rich segregation bands has been obtained on the MA; while complex microstructures are observed for the MMC, including the Cu-rich segregation bands, Al-Si eutectic structure and microsegregation-free structure laid in sequence from the bottom of the melted layer to the top surface. The modelling work suggest that the presence of SiC particles gives rise in high temperatures in the melt pool, which is useful to explain the materials responses upon laser irradiation, such as decomposition of SiC, evaporation of matrix alloy, and oxides formation. The fast cooling rate up to 1011 K/s is responsible for the formation of microsegregation-free structure. Corrosion evaluation has indicated improvement of corrosion resistance of the MMC and the MA after excimer LSM due to the reduction of the intermetallics. For the laser-melted MA, the corrosion behaviour is governed by the surface morphology and the porosity. The significant rippled structure obtained under high laser fluence could lead to crevice corrosion in the valley between the ripples whilst the pores could provide penetrating routes for the chloride solution to reach the Cu-rich segregation bands, leading to the delamination of the melted layer. For the laser-melted MMC, corrosion mainly initiated at the SiC remnants, which are rich in Si. The corrosion sites of the laser-melted MMC are in the form of small cracked blisters.

Yes / In this study, a new double pin tool was utilized for the development of AA6061/316 stainless steel reinforced composite by employing the friction stir processing technique for the first time. The microstructure, hardness, tensile, tribological, and corrosion behaviors of the fabricated composites were investigated and comparative assessments were made with the results obtained from the single-pin tool. The results showed that particle-matrix reaction did not occur in the composites irrespective of the nature of the tool profile. The double-pin tool outstandingly boosted the grain refinement (7.01–5.78 μm), particle fragmentation, and distribution within the Al matrix due to the additional pin-assisted plastic deformation, high straining, dynamic recrystallization, and Zener pinning effects. The double-pin tool improved the microhardness (127–141 HV), tensile strength (162–233 MPa), and corrosion resistance of the composite with respect to the single-pin tool counterparts. The replacement of the single pin tool with a double pin tool diminished the specific wear rate (0.38–0.22 mm3/Nm) of the composite. The double-pin tool has a favourable impact on the structure, mechanical, and corrosion behaviours of the AA6061/316 stainless steel reinforced composite. It is thus recommended for composite development.