The role played by hollow ceramic thin-walled aluminium oxide microballoons on the shear deformation characteristics of AZ31 Magnesium syntactic foam is studied through high-speed machining. The ceramic microballoons embedded in the AZ31 matrix provides the necessary stiffness for these novel foams. The effect of hollow ceramic microballoon properties, such as the volume fraction, thin wall thickness to diameter ratio, and microballoon diameter, profoundly affects the chip formation. A novel force model has been proposed to explain the causes of variation in cutting forces during chip formation. The results showed an increase in machining forces during cutting AZ31 foams dispersed with higher volume fraction and finer microballoons. At a lower (Davg/h) ratio, the mode of microballoon deformation was a combination of bubble burst and fracture through an effective load transfer mechanism with the plastic AZ31 Mg matrix. The developed force model explained the key role played by AZ31 matrix/alumina microballoon on tool surface friction and showed a better agreement with measured machining forces.

Friction Stir Back Extrusion (FSBE) is a new sustainable manufacturing process capable of producing fine grained lightweight tubular shapes. The objective of this work is to investigate the impact of rotational speed and feed rate on the mechanical properties, cycle time and power consumption of friction stir back extruded Mg AZ31-B tubes and determine the optimal settings. FSBE experiments and tensile tests were performed to characterize the mechanical properties of the produced tubes. The investigation is conducted utilizing Response Surface Methodology (RSM) and desirability multi-response optimization technique. Results suggest that ultimate tensile strength and toughness are impacted by both rotational speed and feed rate and are more sensitive to speed. However, both process parameters did not show a significant statistical impact on elongation. Optimal parameters for mechanical properties were identified at a rotational speed of 1767 rpm and feed rate of 102 mm/min. The optimal settings to maximize mechanical properties, minimize power consumption, and maximize productivity were 2000 rpm and 116 mm/min.

Friction Stir Back Extrusion (FSBE) is a new grade of severe plastic deformation process capable of producing metallic tubular geometries that exhibit ultrafine grain structure and superior mechanical properties. FSBE of tubular sections provide opportunities for producing lightweight rigid structures for the automotive, aerospace and construction industries. This research investigates the effect of submerging conditions (in water at 25 °C and 2 °C) for Magnesium AZ31-B tubes on the grain size, mechanical properties, temperature history and power consumption. Submerged FSBE is compared to FSBE in air at fixed process parameters of 90 mm/min and 2000 rpm. It is shown that the impact of submerging is statistically insignificant in terms of the mechanical properties, ultimate tensile strength and percent elongation, of the produced tubes according to the conducted t-tests. On the other hand, the optical microscopy results indicated finer grains at the inner wall of the seamless tubes for FSBE in air and underwater FSBE at 25 °C when compared to underwater FSBE at 2 °C.