Microstructure and corrosion evolution of additively manufactured aluminium alloy AA7075 as a function of ageing

Abstract

Additively manufactured high strength aluminium (Al) alloy AA7075 was prepared using selective laser melting (SLM). High strength Al-alloys prepared by SLM have not been widely studied to date. The evolution of microstructure and hardness, with the attendant corrosion, were investigated. Additively manufactured AA7075 was investigated both in the "as-produced" condition and as a function of artificial ageing. The microstructure of specimens prepared was studied using electron microscopy.Production of AA7075 by SLM generated a unique microstructure, which was altered by solutionising and further altered by artificial ageingresulting in microstructures distinctive to that of wrought AA7075-T6. The electrochemical response of additively manufactured AA7075 was dependent on processing history, and unique to wrought AA7075-T6, whereby dissolution rates were generally lower for additively manufactured AA7075. Furthermore, immersion exposure testing followed by microscopy, indicated different corrosion morphology for additively manufactured AA7075, whereby resultant pit size was notably smaller, in contrast to wrought AA7075-T6.

Mechanical characterization and properties of laser-based powder bed–fused lattice structures: a review

“…Nevertheless, aluminum alloys have low density and high strength, making this material the most used structural material with iron and steel [66]. Moreover, when processed, some alloys can present a better corrosion resistance than the wrought [67]. The majority of the alloys used in PBF-LB are based on commercial grade alloys [66].…”

Review of Powder Bed Fusion Additive Manufacturing for Metals

“…Pits formed in SLM produced AA7075 after corrosion tests were remarkably smaller in comparison to those upon wrought AA7075-T6 due to its finer microstructural features and the absence of large constituent particles. In the as-built AA7075 condition, pits were more pronounced along melt pool boundaries, while they were uniformly distributed in the solutionized sample, and the following ageing caused larger pits along grain boundaries than those within grains [291] The EBM technology offers unique features that other additive manufacturing technologies or even traditional manufacturing methods cannot offer. One of these is the in-process heat treatment capability through the utilization of the elevated build temperature and precise melt pool temperature control.…”

“…Another study worked to prepare crack-free 7xxx Al alloys through co-incorporation of submicron Si and TiB2 into the alloys [290]. Gharbi et al [291] reported the microstructure of as-SLMed AA7075 containing the quasi-crystalline phase (ν-phase) as the principal nano-structural feature. Solution heat treatment dissolved the quasi-crystalline ν-phase and ageing led to precipitation of η -phase (MgZn 2 ) within grains and along grain boundaries, revealing columnar grains in the microstructure of AA7075 alloy.…”

“…There are limited studies on the corrosion behavior of powder bed fusion additive manufactured Al alloys [279,291,317]. Bi et al [279] evaluated the corrosion performance of the SLM-fabricated Al-14.1Mg-0.47Si-0.31Sc-0.17 Zr alloy in comparison to its heat-treated counterpart in 3.5 wt.% NaCl solution.…”

How build angle and post-processing impact roughness and corrosion of additively manufactured 316L stainless steel

“…Several other examples of microstructural features and processing defects that have been investigated are; nanoscale oxides/inclusions 7,20,23,24 , solute segregation (i.e. cell boundaries, melt pool boundaries) 7,13,[22][23][24][25][26][27][28][29] , texture and grain character 29 , residual stresses 3,30,31 , surface roughness 18,20,[32][33][34][35] , and porosity 7,9,[18][19][20][21][22] .…”