Additive Friction Stir-Enabled Solid-State Additive Manufacturing for the Repair of 7075 Aluminum Alloy

Abstract

The repair of high strength, high performance 7075 aluminum alloy is essential for a broad range of aerospace and defense applications. However, it is challenging to implement it using traditional fusion welding-based approaches, owing to hot cracking and void formation during solidification. Here, the use of an emerging solid-state additive manufacturing technology, additive friction stir deposition, is explored for the repair of volume damages such as through -holes and grooves in 7075 aluminum alloy. Three repair experiments have been conducted: double through-hole filling, single through-hole filling, and long, wide-groove filling. In all experiments, additive friction stir deposition proves to be effective at filling the entire volume. Additionally, sufficient mixing between the deposited material and the side wall of the feature is always observed in the upper portions of the repair. Poor mixing and inadequate repair quality have been observed in deeper portions of the filling in some scenarios. Based on these observations, the advantages and disadvantages of using additive friction stir deposition for repairing volume damages are discussed. High quality and highly flexible repairs are expected with systematic optimization work on process control and repair strategy development in the future.

Additive friction stir deposition: a deformation processing route to metal additive manufacturing

“…For example, feedstock made from aluminum alloys (e.g. 2xxx [36,55], 6xxx [31], and 7xxx [49,56]) with a coarse microstructure (grain size ∼ 100-200 μm) may have their grain size reduced to 1-5 μm after AFSD. Figure 2(b) shows an example for AFSD of AA2024, with a comparison of the microstructure before and after printing.…”

“…The most promising market for AFSD thus lies in where excellent mechanical properties are highly desired and minimal post-processing heat treatment is preferred. In terms of materials, AFSD has particular advantages in processing and manufacturing of high-strength aluminum alloys that suffer from hot cracking issues in fusion-based additive manufacturing [36,49,55,56].…”

“…One niche application of AFSD is the structural repair of components for the aerospace and defense industries, in which load-bearing components may suffer from corrosion, wear, or other damages. Griffiths et al [56] explored the through-hole and groove filling of AA7075 plates and showed that AFSD was effective at filling the entire volume. Sufficient mixing was observed between the deposited material and the sidewall of the feature; as a result, the interface was indiscernible with a gradual change in microstructure.…”

“…(c) A micrograph of the repair region showing a curved interface between a fine, equiaxed microstructure (filled material) and a rolling microstructure (side wall). Images reproduced with permission from reference[56]. (d) Illustration of the recycling process using AFSD.…”

Repair of Aluminum 6061 Plate by Additive Friction Stir Deposition

“…AFSD has obvious potential for repair applications; however, only two publications were identified that directly assess implementation strategies [3,38]. Griffiths, et al, evaluated AFSD for hole-and groove-filling in of 7075 aluminum plate, and reported complete filling of the features combined with extensive feed/substrate mixing and good bonding in the upper portions of the repair.…”