Assessing single and multi-step friction stir consolidated recycled billets through uniaxial upsetting test

Abstract

Friction stir consolidation (FSC) represents a solid-state recycling technique that directly transforms machining waste into billets by the stirring action and friction heat of the rotating tool. This technology has demonstrated superior energy efficiency compared to remelting based traditional recycling methods. Concerning the FSC process mechanics, they impart temperature, strain and strain rate gradients across the billet sections leading to variations in mechanical properties such as hardness values and grain size distribution. Therefore, multi-step FSC variants were introduced to eliminate this inherent inhomogeneity inside the billets of the single-step FSC approach. However, the billets manufactured by multi-step methods showed better mechanical properties, and gradation across the billet section still persisted. This property led to the evolution of friction stir consolidation as a new manufacturing method for developing functionally graded materials. Previously, the gradation was highlighted by the Vickers hardness test and grain size distribution. Therefore, in the ongoing study, an advanced characterization technique was adopted by extracting miniaturized samples from the section of FSC billets and subjected them to the upsetting test. Employing advanced characterization techniques to get insights into the gradation and quality of billets manufactured through various process variants and will allow to draw a better conclusion regarding adoption of a more suitable FSC process variant