Jorge F. dos Santos

Crystallographic Texture in Bobbin Tool Friction-Stir-Welded Aluminum

Bobbin tool friction-stir welding was used to join 3.2-mm-thick AA2198. The textural results show that four sub zones are formed vertically in the stirred zone. The materials in upper and lower two zones underwent negative and positive shears, respectively; they are uniformly recognized as dominate C and minor A simple shear components.

Influence of Cu/Li Ratio on the Welding Forces and Mechanical Properties of Two Bobbin Tool Friction Stir Welded Al-Cu-Li Alloys

AbstractIncreasing space activities produce a high number of space objects and lead to increasing collision risks which urges leading industries to look for future removal strategies. Material substitution in order to raise demisability during atmospheric reentry is a possible solution. Modern aluminum lithium alloys are under consideration to replace high-temperature melting materials like titanium. Further, friction stir welding was proposed as suitable joining technology in order to avoid high heat inputs during manufacturing. In this work, two modern Al-Li-Cu alloys, AA 2060 and AA 2196, in peak-aged temper were welded using the stationary shoulder variant of bobbin tool friction stir welding. Identical process parameters led to defect-free welds in both alloys. The macrostructural and microstructural features are shown and analyzed. The welds were mechanically tested to an efficiency of 78 and 70% of the base metal ultimate tensile strength for AA 2060 T8 and AA 2196 T8, respectively. The process forces as well as the thermal cycle experienced by the workpiece material were used to explain the mechanical performance. The difference in composition regarding the Cu/Li ratio of the alloys was taken into account when the mechanical properties were correlated with the thermally affected microstructure of the weldments.

Filling, Feeding and Defect Formation of Thick-Walled AlSi7Mg0.3 Semi-Solid Castings

Aluminium semi-solid castings have gained increased attention due to their superior mechanical properties, lower porosity compared to conventional high pressure die cast material. These characteristics suggests that semi-solid casting should be suitable to produce thick-walled structural components, yet most successful applications of semisolid casting have been for thin-walled components. There is a lack of understanding on filling and feeding related defect formation for semi-solid castings with thick-walled cross-sections. In the current study an AlSi7Mg0.3 aluminium alloy was used to produce semi-solid castings with a wall thickness of 10mm using a Vertical High Pressure Die Casting machine. The RheoMetalTM process was used for slurry preparation. The primary solid α-Al fraction in the slurry was varied together with die temperature. The evaluation of the filling related events was made through interrupted shots, stopping the plunger at different positions. Microscopy of full castings and interrupted test samples were performed identifying the presence of surface segregation layer, shear bands, gas entrapment, shrinkage porosity as well as burst feeding.

Microstructure in Dissimilar Friction Spot Weld of Al to Mg Alloys Observed by Stop-Action Technique

In the current study, the formation of intermetallic compounds in dissimilar friction spot welding (refill friction stir spot welding) of AA5754 aluminum alloy to AZ31 magnesium alloy has been investigated by applying a stop action technique. The welding cycle was forced to stop during the dwell time, and subsequently, the weld was quenched by pouring a mixed solution of ice and water to freeze the microstructure. A large volume of eutectic structure was observed in the weld center of the stop action sample due to mutual diffusion of Al and Mg atoms induced by plastic deformation. During the sleeve retraction, a redistribution of eutectic structure and Mg alloy, and extensive diffusion led to an inhomogeneous intermetallic phase distribution in the Al top sheet.