Energy Density Effect of Laser Alloyed TiB2/TiC/Al Composite Coatings on LMZ/HAZ, Mechanical and Corrosion Properties

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.

Možni ukrepi za zmanjševanje morske mikrobiološke korozije

“…To lahko pripišemo manjši trdoti aluminijeve zlitine ter pojavu luknjičaste in splošne korozije na vzorcih iz nizkoogljičnega jekla, ki so mikroorganizmom onemogočili pritrditev na površino. Kot so ugotovili Dunja Ravnikar in sodelavci [46], so aluminijeve zlitine v splošnem dobro odporne na korozijo, vendar se ob prisotnosti klorovih, fluorovih, jodovih in bromovih ionov v mediju zviša aluminijeva občutljivost na lokalno korozijo. Poleg tega dodatno izpostavljenost korozijskim napadom povzroča tudi aluminijeva nizka gostota in slabe tribološke lastnosti.…”