AA7075 high-strength aluminum alloy, which has many applications in the aircraft, marine and automobile industries, happens to be susceptible to stress corrosion cracking (SCC) when exposed to corrosive environments, resulting in reduced service life of the components. Inappropriate fabrication processes may augment this behavior. The fabrication of AA7075 components using conventional fusion welding processes may produce defects that include hot cracking and porosity. Friction stir welding (FSW) is a solid-state joining process that can avoid these problems and being widely used for components made of aluminum alloys. Because the joining occurs at a temperature that is lower than the melting point of the material, solidification cracking defects can be eliminated. This study investigates the SCC behavior of FSW AA7075-T651 joints. Horizontal-type SCC test was conducted on circumferential-notched tensile (CNT) specimens exposed to 3.5 wt. % NaCl solutions under various axial stress conditions. The different regions of the fractured specimens, such as the machined notch, SCC region and region of ultimate mechanical failure were analyzed by scanning electron microscopy (SEM) to establish the mechanism of SCC. The threshold stress of parent metal (PM) and stir zone (SZ) of the FSW joint were found to be 242 and 175 MPa, respectively.
Stir cast aluminum based metal matrix composites (MMCs) with silicon carbide (SiC) reinforcement particles consist of cast product dendrites and large agglomerated reinforcements. The agglomeration of SiC particles creates a difference in properties in the composite system. Friction stir processing (FSP) is used to overcome the uneven distribution of SiC particles in the aluminum matrix. The friction stir processed (FSPed) microstructure is significantly influenced by the process parameters used for processing. In FSP, the effect of the tool diameter ratio (tool shoulder diameter to pin diameter) on material flow, material mixing, material consolidation is more predominant than other parameters. Hence, a perfect combination of shoulder diameter to pin diameter is required to produce sufficient material flow. In this investigation, the tool diameter ratio is varied from 2.0 to 4.0 for processing composite material and thus FSPed zones were subjected to micro structural characterization. It was concluded that a tool diameter ratio of 3.0 yielded a defect free stir zone with higher hardness compared to other ratios.
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