Mechanical characterization of spot friction stir welded joints in aluminum alloys by combined experimental/numerical approaches: Part I: Micromechanical studies

This paper is part I of a two part paper, which summarizes recent studies carried out to characterize the weld zone mechanical properties in aluminum alloy 6111 spot friction stir welded joints at both the macromechanical and micromechanical levels. In this paper, micromechanical level investigations are reported for joints welded with different processing times. Apart from microstructural studies and microhardness tests, a new approach to characterize the distribution of weld zone modulus using modal vibration tests on micron scale cantilever array specimens with a micro-scanning laser vibrometer and the corresponding finite element simulations has been developed. Microcantilever array samples were designed in such a way that each microcantilever represents one of the weld zones. Microscopic studies reveal a partial metallurgical bond formed in the direction of flow, which is governed by the tool used and Vickers hardness numbers in those regions were found to be considerably lower than those of the base metal. From the analysis of microcantilever arrays, it was concluded that the variation of modulus in the weld zones is minimal and there is no significant reduction in the weld zone modulus when compared to that of the base metal.