Repair of aluminum alloy 7075 using laser based directed energy deposition additive manufacturing and laser peening

Aluminum alloy (AA) 7075 is commonly used in many structural parts in aerospace applications. During their life cycle, these structural parts can become damaged due to wear and corrosion, which limits their overall service life. The useful life of the structural parts could be enhanced through the repair of the damaged region. This paper investigates the potential of laser based directed energy deposition (LDED) as a repair process for AA 7075. The repair process was demonstrated on AA 7075 substrates that had machined divots representing the damaged region to be repaired. A systematic LDED process was developed to repair the divot blend that consisted of depositing an intermediate layer of AlSi10Mg alloy, a near-eutectic alloy with a low solidification temperature to help avoid solidification cracking, and filling the remaining divot with an Al-Mg-Sc alloy. With postrepair laser peening (LP) treatment, the fatigue life of the repaired coupons was improved to about four times the baseline value. The significant increase in the fatigue life after LP appeared to be the result of a combination of factors. LP has been shown to provide substantial improvement in the fatigue life by introducing near-surface compressive residual stresses. In addition, microstructural analysis indicated that the LP treatment helped reduce and partially heal the near-surface defects that were present within the repair region after the LDED repair. Finally, LP appeared to induce a slightly higher hardness near the surface of the repair.