Uroš Trdan

Surface modification of laser‐ and shot‐peened 6082 aluminium alloy

Purpose – The purpose of this paper is to investigate the effect of shock waves and strain hardening effect of laser and shot peening on precipitation‐hardened aluminium alloy AA 6082‐T651.Design/methodology/approach – The hardened layer was evaluated by means of surface integrity with optical microscopy, scanning electron microscope (SEM), energy dispersive spectroscopy, analysis of microhardness and residual stress profiles. Corrosion anodic polarization tests in a 3.5 per cent NaCl water solution were carried out to express a pitting potential and the degree of pitting attack, which was verified on SEM and with 3D metrology.Findings – Research results indicated significant differences between two treatment techniques which had an important influence on the final condition of the surface layer. Potentiodynamic polarization tests inferred that laser peening enabled shift of the pitting potential to more positive values, which ensures higher corrosion resistance.Originality/value – Results confirmed that ...

Laser Shock Processing of ENAW 6082 Aluminium Alloy Surface

The present paper treats results of laser shock processing applied to a precipitationhardened ENAW 6082-T651 aluminium alloy. Processing was performed with a Nd:YLF-yttrium lithium fluoride crystal laser with power densities of 2 and 4 GW/cm2, producing a pulse of 18 ns. Laser shock processing experiments were performed with the closed ablation method, the application of an ablative coating and a transparent tamping medium to obtain a higher shock-wave pressure. In the first phase, the surface study focused on the record of surface profile with a roughness gauge and on an evaluation of surface topography at a scanning electron microscope. In the second phase, residual stresses were measured using the relaxation hole-drilling method at a processed specimen surface. Then followed measurement of microhardness in the cross section. The hardening results obtained were evaluated on the basis of variations of residual stresses and of microhardness, and of macro and microstructural changes of the surface, i.e. the surface layer. The purpose of processing was to improve fatigue strenght and, consequently, extend the life of a machine component in operation.

Generation of Residual Stresses and Improvement of Surface Integrity Characteristics by Laser Shock Processing

The influence of different parameters of laser shock processing applied to a precipitation-hardened aluminium alloy 6082-T651, on residual stress, surface tophraphy and microhardness was investigated. Processing was performed with an innovative Nd:YLF laser with the power densities of 2 and 4 GW/cm2, with a uniform pulse duration of 18 ns. Laser shock processing experiments were performed with the closed ablation method to ensure a higher shock-wave pressure. In the first phase, the study was focused on an evaluation of surface topography, with the record of the surface roughness profile and with the surface evaluation at a scanning electron microscope JEOL JXA-8600M. Then followed measurement of microhardness HV0.2 in the cross section region. In the second phase comparison of residual stresses which were measured using the X-ray diffraction, was performed. Laser shock processing turned out to be a very efficient technique to improve surface properties. On the basis of the micro plastic deformation induced by shock waves, an increased dislocation density in the specimen surface was obtained. The gradient of dislocation piling through the specimen depth improved the variation of microhardness and residual stresses, which, in turn, improves fatigue strength of the material under dynamic loading.

Analysis of residual stress and corrosion resistance of laser shock-processed 6012 and 6082 aluminium alloys

The paper provides a thorough analysis of a surface layer prior to and after Laser Shock Processing under different parameter conditions. Optimum conditions were determined using a factorial design aided with an analysis of variance (ANOVA). As the first experimental factor, pulse density with 900 and 2500 pulse/cm2 was chosen. The second factor was the type of material, i.e. aluminium alloys ENAW 6012 and ENAW 6082. Evaluation of different conditions of specimen treatment was made using three response variables, i.e. surface roughness, magnitude of residual stresses, and corrosion resistance given by pitting potential (Epitt). A thorough analysis of the modified surface layer was made with measurement of microhardness, and with images obtained in optical and electronic microscopy (SEM) and energy dispersion spectroscopy (EDS) to determine corrosion products around the pits formed after corrosion testing. The experiments confirmed characteristic influences of individual LSP parameters on properties of the treated material surfaces. ENAW 6012 aluminium alloy showed better corrosion resistance than ENAW 6082 alloy with lower pitting attack at its surface. Corrosion tests showed that a higher pulse density produces shifting of the pitting potential to more positive values, which ensures higher corrosion resistance from the viewpoint of preserving a passive protecting film on the surface layer.