A new approach of direct recycling of aluminium alloy chips (AA6061) in hot press forging process

This study introduces a new approach of direct recycling using the hot press forging process that eliminates the two intermediate processes of cold-compact and preheating. Thereby, it leads to low energy consumption without intervening the metallurgical processes. The mechanical and physics properties of AA6061 aluminium alloy recycled by solid-state recycling were investigated. Amounts of oxide in recycled chips were measured by using oxygen-nitrogen analyser. Oxygen concentration in the recycled specimens increased proportionally with the total surface area of the machined chip per unit volume. The performance of recycled aluminium chip on their mechanical properties and microstructure were compared with the reference specimen. The recycled specimens exhibited a remarkable potential in the strength properties (Ultimate Tensile Strength, UTS = 30.73-117.85 MPa, Elongation to Failure, ETF = 3.84-11.84 %) where it increased with increment of total surface area of chips. This is mainly attributed to grain refinement (7.9019.50µm) of the microstucture. On the other hand, recycled specimens with medium surface area of chips posed highest elongation to failure (11.84%). Grain size and oxide amount of billet have an effect on the elongation of recycled materials. Analysis for different operating temperatures showed that the higher temperatures (520°C) gave better result on mechanical properties (UTS = 117.85 MPa) and finer microstructure (7.90µm). In this study, the recycled AA6061 chip showed the good potential as the comparison of using only 17.5% of suggested pressure where 70.0 MPa (maximum operating pressure) from 400.0 MPa (suggested optimum pressure) exhibited 35.8% the ultimate tensile strength where 117.85 MPa (maximum tensile strength for recycled billet) from 327.69 MPa (reference). This proved that hot forging process could be an acceptable alternative method for recycling of AA6061 aluminum alloy chips