| Abstract Scope |
Aluminum 7075 is a high strength, lightweight alloy making it desirable for many applications in the transportation and aerospace industry. The use of this alloy in welded and additively manufactured (AM) structures has been historically constrained by its elevated susceptibility to solidification cracking. New consumables with ceramic particle inclusions, also called nanoparticles or inoculants, have been developed which promote fine equiaxed grains to form during deposit solidification. These deposits have been found to be solidification cracking resistant with different modes of the gas metal arc directed energy deposit (DED) process. The effects of inoculants on other properties such as fatigue and stress corrosion cracking (SCC) were unknown. The purpose of this investigation was to develop microstructure – property (tensile, fatigue, SCC) relationships for different wire arc DED processes using inoculated 7075 wire and argon shielding. In particular, the effect of process and metal transfer on microstructure (grain size, inoculant size & morphology) needed factored into the relationships. Single-pass per layer walls were constructed using reciprocating wire feed (RWF) (i.e tradename Cold Metal Transfer (CMT)) and pulse gas metal arc (GMA) DED processes. Half of each DED build underwent a T73 condition heat treatment while the other half remained in the as-deposited condition for evaluation. Tensile and fatigue tests were performed according to ASTM E8 and ASTM E466 respectively. Preliminary results show inoculated 7075 DED material has good yield and ultimate tensile strength after post-build heat treatment compared to wrought 7075 properties. Fatigue testing is in-progress and will be presented along with initial microstructure property relationships. Initial characterization used optical microscopy, energy dispersive X-ray spectrometry (EDS), and SEM. Advanced microstructure characterization, such as TEM will also be used determine effects of inoculant-based particles on these properties. SCC testing is also underway and will be presented later |