Modification of electrical conductivity by friction stir processing of aluminum alloys

A wide range of solid-state manufacturing technologies for joining and modification of material original properties are assuming increasing importance in industrial applications. Among these, friction stir-based technologies are the most significant, namely, friction stir processing (FSP) and friction stir surfacing. The electrical conductivity is a significant property undergoing modification, but this property has not been characterized and fully exploited from the technological point of view. The present work aims to study the electrical conductivity behavior in FSP of aluminum alloys in order to identify the major factors governing this property. FSP was applied on AA1100, AA6061-T6, and AA5083-H111 alloys with different parameters. Electrical conductivity profiles were measured at different depths and compared with hardness profiles and microstructures. It was found that solid-state friction stir processing of aluminum alloys lead to electrical conductivity changes of about 4%IACS (International Annealed Copper Standard). These changes are more intense in heat-treatable alloys than in work-hardenable ones. Higher rotating versus travel speed ratios (a"broken vertical bar/V) induce higher variations in the electrical conductivity. In FSP, the factors governing the electrical conductivity variations are mostly the grain size and the presence of precipitates. It was shown that, for some FSP applications, electrical conductivity may be a process characterization method more precise and meaningful than hardness to assess local material condition.