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A 150 μm thick fully dense Ni coating was deposited on AZ31B magnesium alloy by a newly developed in-situ shot-peening-assisted cold spray process. Strong adhesion strength of Ni coating (>65.4 MPa) was achieved. The present Ni coated AZ31B reveals comparable electrochemical behavior with annealed bulk Ni in 3.5 wt.% NaCl aqueous solution. Long-term immersion test (1000 h) and NaCl salt spray test (1000 h) further verified the robust corrosion resistance of the cold sprayed Ni coating. This work provides a novel green approach for corrosion protection of magnesium alloys. [ABSTRACT FROM AUTHOR]

The influence of artificial ageing on the corrosion behaviour of Cu-4 wt.% Ti alloys in 3.5 wt.% NaCl solution was studied. Corrosion tests showed that ageing treatment changed the corrosion morphology of the alloys. All specimens were susceptible to both intergranular and pitting corrosion. The pitting corrosion susceptibility decreased with increasing ageing time. In particular, the presence of abundant cellular β-Cu 4 Ti precipitates refined microstructures in specimen aged at 773 K for 24 h, providing “enveloping effect” that dramatically improved the corrosion resistance. The corrosion resistance of the aged Cu-4 wt.% Ti alloys followed the order: over-aged > peak-aged > early-aged > solution treated. [ABSTRACT FROM AUTHOR]

Abstract: This study investigates the atmospheric corrosion behaviour of ingot and as-extruded AM60 Mg alloys in a polluted city. The corrosion rate of the ingot samples was higher than that of the extruded samples. The size of dust particle conglomerates adsorbed on the sample surfaces was related to the pit sizes. The main corrosion products of both alloys included MgSO4·6H2O and MgSO3·6H2O. The extruded samples had more homogeneous structures and less second-phase contents compared with the ingot samples. As a result, the corrosion films formed on the extruded samples had better protective effects than those formed on the ingot samples. [Copyright &y& Elsevier]

Abstract: The corrosion behaviour of die-cast AZ91D magnesium alloys in sulphate solutions was investigated by SEM, FTIR and polarization measurements. For immersion times less than 48h, no pitting corrosion occurred and only generalized corrosion was apparent. According to the polarization curves, the corrosion rate order of the die-cast AZ91D Mg alloy in three aqueous solutions was: NaCl>MgSO4 >Na2SO4. The main corrosion products were Mg(OH)2 and MgAl2(SO4)4·22H2O in the sulphate solutions and the product film was compact. Precipitation of MgAl2(SO4)4·22H2O required a threshold immersion time. [Copyright &y& Elsevier]

• Three Ni powders were sprayed on AZ31B by cold spray for corrosion protection. • Coating microstructures and corrosion performances were correlated with powder feature. • Powder surface protruding granules will hinder inter-particle intimate contact. • The gas-atomized smooth Ni powder can give > 3000 h corrosion protection for AZ31B. Three nickel (Ni) powders, i.e. gas-atomized spherical Ni (GA-Ni), carbonyl irregular Ni (C-Ni), and electrolytic dendritic porous Ni (E-Ni), were sprayed on magnesium alloys by an in-situ micro-forging assisted cold spray method. Although all deposited coatings present extremely low porosity, the C-Ni and E-Ni coatings reveal poorer inter-particle bonding than GA-Ni coating. Electrochemical tests reveal that the inter-particle gaps will act as fast pathways for the corrosive media to penetrate the coatings, thereby the GA-Ni coating with intimate inter-particle boundaries can isolate the corrosive media for 3000 h and the C-Ni and E-Ni coatings fail after <10 h corrosion. [ABSTRACT FROM AUTHOR]

Surface-porous Mg–Al alloys with different microstructures were fabricated via a new method of electrochemical dealloying in a neutral 0.6M NaCl solution. A bimodal porous structure with 47.57 ± 11.43 μm large pores and 265.60 ± 78.68nm honeycomb-like fine pores was obtained by direct electrochemical dealloying of as-cast Mg 80 Al 20 alloy. Following annealing, the eutectic structure disappeared and a bicontinuous, single-sized, porous structure with 7.10 ± 1.96 μm ligaments was created by an annealing-electrochemical dealloying approach. The porous formation mechanism is governed by selective dissolution of the α-Mg phase, which leaves the Mg 17 Al 12 phase as the porous layer framework. [ABSTRACT FROM AUTHOR]

The effect of the Mo element on the intergranular corrosion behavior was investigated on super-austenitic stainless steels. The σ-phase structure and compositional changes of stainless steels with different Mo contents during aging at 800–900°C were investigated by TEM, combined with electrochemical tests, and two different intergranular corrosion mechanisms were revealed. The low-Mo 904 L stainless steel induces severe intergranular electrochemical corrosion due to selective anodic dissolution at grain boundaries caused by decreased passivation ability and σ-phase composition changes. The σ-phase precipitation of 254SMo and AL-6XN with high-Mo leads to Cr and Mo depletion reduces passivation film continuity, and causes intergranular corrosion. • Aging coarsens the σ-phase at grain boundaries in super austenitic steels with higher Mo content. • Low Mo austenitic steels face intergranular corrosion from weakened boundary passivation. • High Mo steels suffer intergranular corrosion from Cr/Mo depletion and erratic passivation. • Precipitate morphology and composition significantly alter intergranular corrosion. [ABSTRACT FROM AUTHOR]

Abstract: The atmospheric corrosion behaviour of cast and high pressure die-cast AZ91D alloy in a polluted environment were investigated by SEM, XRD and FTIR. The atmospheric corrosion rate of the ingot was higher than that of the die-cast specimen. SO2 gas played an important role in atmospheric corrosion. The effects of dew condensation on the ingot were greater than that on the die-cast specimen. The corrosion was initiated in the less noble α phase of the samples. The β phase, on the other hand, remained and acted as a barrier to corrosion. [Copyright &y& Elsevier]