Friction surfacing of aluminum alloys on Ti6Al4V - Investigation of process parameters, material deposition behavior and bonding mechanisms

Abstract

This study addresses a detailed investigation of friction surfacing (FS) process parameters for two materials with low metallurgical compatibility, i.e. Al and Ti, to achieve successful depositions, representing a very challenging task. The difference in suitable process parameters between two Al alloys onto Ti is highlighted. For instance, AA6082 requires higher rotational speeds than AA7050, resulting in higher process temperatures that lead to the formation of intermetallics with a thickness of about 0.3 $\mu$m at the interface. This indicates that diffusion is the main bonding mechanism for AA6082, while mainly mechanical interlocking contributes to bonding for AA7050. Additionally, AA6082 presents slightly thicker ($\sim$240 $\mu$m) and wider ($\sim$28 mm) layers than AA7050 ($\sim$185 $\mu$m and $\sim$24 mm, respectively). Based on the experimental results, a new theory of material deposition is proposed for the dissimilar Al/Ti material combination, as a unique deposition behavior could be identified. The experiments show that material is deposited only in the peripheral areas of the stud, but not in the center, as typically seen in FS. Higher local process temperatures in the peripheral areas result in lower local flow stresses, which increase stud shearing and thus deposition of the plasticized stud material.