Microstructure Features and Mechanical Properties of Single-Pass Multilayer 6061 Aluminium Alloy Based on Friction Extrusion Additive Manufacturing

The friction extrusion additive manufacturing (FEAM) process of 6061 aluminium alloy was successfully performed. The microstructure features, interface bonding mechanism and mechanical properties of single-pass one-layer, two-layer and nine-layer additive specimens were discussed in detail. It is found that under the process conditions of a spindle speed of 600 r/min and a moving speed of 300 mm/min, completely dense and defect-free 6061 one-layer, two-layer and nine-layer additive specimens with layer thickness and width of 4 and 32 mm are obtained. The uniform microstructures of additive specimens are composed of fine equiaxed grains. The average grain size of one-layer and nine-layer additive specimens are 5.63 +/- 1.66 pm and 8.31 +/- 1.67 pm, respectively, which are significantly refined compared with the bar base metal (24.21 +/- 5.3 pm). In the microstructures of single-pass one-layer additive specimen, the main strengthening phase beta" is almost completely dissolved and phase g is coarsed, so the average hardness is 64.7% of the bar base metal. The additive interface realizes metallurgical bonding and has the most significant degree of grain refinement. The hardness of interface reduce to 56.9% of the bar base metal because the strengthening phases beta" and beta are almost completely dissolved. The average hardness of nine-layer specimen after multiple thermal cycles is 50.6% of the base metal. The nine-layer additive specimen exhibits excellent strength and toughness matching. The average tensile strength and elongation along the length direction of the additive specimen are 194.25 MPa and 34.6%, respectively, and the average tensile strength and elongation along the vertical direction of the additive specimen are 151.0 MPa and 10.4%, respectively.