Abstract
In the present work, TiC/TiB2/Al composite coatings were synthesized onto a precipitation hardened AlSi1MgMn alloy by laser surface alloying (LSA), using 13.3 J/mm2 and 20 J/mm2 laser energy densities. Microstructure evaluation, microhardness, wear and corrosion performance were investigated and compared with the untreated/substrate Al alloy sample. The results confirmed sound, compact, crackles composite coating of low porosity, with a proper surface/substrate interface. Microstructural analyses revealed the formation of extremely fine nano-precipitates, ranging from of 50–250 nm in the laser melted (LMZ) and large precipitates, accompanied with grain coarsening in the heat-affected zone (HAZ), due to the substrate overheating during the LSA process. Nonetheless, both coatings achieved higher microhardness, with almost 7-times higher wear resistance than the untreated sample as a consequence of high fraction volume of hard, wear resistant TiB2 and TiC phases inside the composite coatings. Further, cyclic polarization results in 0.5 M NaCl aqueous solution confirmed general improvement of corrosion resistance after LSA processed samples, with reduced corrosion current by more than a factor of 9, enhanced passivation/repassivation ability and complete prohibition of crystallographic pitting, which was detected with the untreated Al alloy.
Highlights
Aluminium alloys are used extensively in automobile and aerospace applications mainly due to good strength-to-weight ratio, ductility, lightweight, availability and low cost [1,2,3,4]
Cyclic polarization results in 0.5 M NaCl aqueous solution confirmed general improvement of corrosion resistance after laser surface alloying (LSA) processed samples, with reduced corrosion current by more than a factor of 9, enhanced passivation/repassivation ability and complete prohibition of crystallographic pitting, which was detected with the untreated Al alloy
Was efficiently melted, which is of utmost importance to obtain good adhesion between coating and Measurements of the laser melted zone (LMZ) depth revealed that the thickness of LMZ increases the substrate material
Summary
Aluminium alloys are used extensively in automobile and aerospace applications mainly due to good strength-to-weight ratio, ductility, lightweight, availability and low cost [1,2,3,4]. Metals 2020, 10, 411 high hardness, low density, high melting temperature and good wear and corrosion resistance, ceramics such as carbide, oxide and boride (SiC, TiO2 , WC, TiC and TiB2 ) are frequently used as the coating material on Al alloys [2,7,8,9,10,11,12,13,14,15,29]. Al alloys and novel way excellentMMC wear (metal and corrosion resistant MMC (metal matrix composite) coatings oncommercial various Alapplications, alloys andespecially, promote in their commercial and applications, promote their the automotive processingespecially, industry. Al alloys and novel way excellentMMC wear (metal and corrosion resistant MMC (metal matrix composite) coatings oncommercial various Alapplications, alloys andespecially, promote in their commercial and applications, promote their the automotive processingespecially, industry. in the automotive and processing industry
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