# Influence of Laser Shock Peening without Coating on Surface, Mechanical, Corrosion, and Tribological Characteristics of AA7075/h-BN Nanocomposites

## TL;DR

This paper studies how laser shock peening improves the surface and mechanical properties of AA7075 nanocomposites for aerospace and automotive use.

## Contribution

The study introduces laser shock peening without coating as a novel method to enhance the performance of AA7075/h-BN nanocomposites.

## Key findings

- LSPwC increased surface hardness by 7-13% due to grain refinement and compressive residual stress.
- Surface roughness decreased by 12% in LSPwC-treated AA7075/h-BN composites.
- Tribological performance improved, with the lowest specific wear rate and coefficient of friction observed in AA7075/1.0h-BN composites.

## Abstract

AA7075 metal matrix composites have been widely used
for their
high strength-to-weight ratio. However, their relatively poor surface
and tribological characteristics restrict their wider application
in aerospace and automotive components. This study investigates the
effect of laser shock peening without coating (LSPwC) on surface,
mechanical, corrosion, and tribological properties of stir-squeeze
cast AA7075, AA7075/0.5h-BN, and AA7075/1.0h-BN nanocomposites. LSPwC
was carried out using a 1064 nm wavelength, 400 mJ laser pulse energy,
7.95 GW/cm2 power density, and 75% overlap. The LSPwC-treated
specimens exhibited a significant improvement in surface hardness
of ∼7% for as-cast AA7075 and ∼13% for AA7075/h-BN MMCs,
primarily due to grain refinement, induced compressive residual stress
(CRS), and intermetallic compound (IMC) strengthening. A reduction
in surface roughness (R
a) of ∼12%
was observed in LSPwC-treated AA7075/h-BN in contrast to that in AA7075.
Corrosion characteristics were enhanced through the formation of a
stable and uniform passive oxide layer, thereby minimizing pitting
corrosion in sacrificial anodic environments. The synergistic effect
of h-BN and LSPwC enhanced surface wettability and tribological characteristics,
resulting in a transfer of severe abrasive, adhesive, and delamination
wear into predominantly milder adhesion and delamination wear. Overall,
LSPwC-treated AA7075/1.0h-BN composites obtained the lowest SWR (0.1813
mm3/KN-m at RT and 0.8233 mm3/KN-m at 150 °C)
and CoF (0.294 at RT and 0.314 at 150 °C).