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Panels coated by hot dipping with zinc (HDG), Zn-5Al (Galfan) and Zn-1.5Al-1.5Mg coatings at different thicknesses were phosphated and painted on an industrial line. Crevice panels with non-painted bare parts modelling conditions in hem flanges, reference panels with open surfaces and formed non-painted panels were exposed to a cyclic accelerated automotive test. Zn-Al-Mg coatings with the thickness of 10 mm provided similar or even better protection than HDG and Galfan at 20 mm in both confined and open configurations. In comparison to 10-mm HDG, the Zn-Al-Mg coating delayed red rust appearance in crevices by a factor of 2 and the maximal depth of corrosion in the steel substrate was by 42% lower. Confined areas were more corroded than open surfaces. For HDG, the time to red rust appearance dropped by 50-75%, corrosion attack in steel was from 3.5 to 7 times deeper and mass gain was about 2.3 times higher in crevices than on open surfaces. Corrosion of Zn-Al-Mg may be more affected by local environmental conditions created by the crevice configuration than for HDG. Red rust appearance on formed panels of 20-mm Galfan, 7-, 10-and 14-mm ZnAl-Mg was delayed to 10-mm HDG by a factor of 2.8, 3.5, 3.8 and >4.5, respectively. No adverse effect of forming was noticed. The results indicate that 2-to 3-fold reduction of the coating thickness for Zn-Al-Mg alloy coatings in comparison to traditional HDG may be possible without compromising the corrosion performance.

According to market data, about 15% of world zinc consumption is devoted to the production of zinc-base alloys that are used for manufacturing automotive parts, electronic/electrical systems and also, water taps and sanitary fittings, household articles, fashion goods, etc. These alloys are characterized by low melting points and high fluidity that make them suitable for foundry applications. Typically, they are processed by hot chamber high-pressure die-casting where can be cast to thicknesses as low as 0.13 mm. The die-cast zinc alloys possess an attractive combination of mechanical properties, permitting them to be applied in a wide variety of functional applications. However, depending on the alloying elements and purposes, some zinc alloys can be processed also by cold chamber die-casting, gravity, or sand casting as well as spin casting and slush casting. In this paper, a detailed overview of the current knowledge in the relationships between processing, microstructure and mechanical properties of zinc-base alloys will be described. In detail, the evolution of the microstructure, the dimensional stability and aging phenomena are described. Furthermore, a thorough discussion on mechanical properties, as such as hardness, tensile, creep, and wear properties of zinc-base alloys is presented.Metals 2020, 10, 253 2 of 16 melting temperature, resulting in low energy consumption and long die life, combined with high fluidity, that helps in filling complex mold cavities and very thin sections, typically as low as 0.75 mm or even down to 0.13 mm [7]. They show good mechanical properties, including equivalent, or often better, bearing and wear properties than conventional Cu alloys [8,9]. Additionally, they offer good finishing and ability to be easily plated, making them more resistant to corrosion and wear and improving their aesthetic appearance. On the contrary, they suffer from reduction in performance above 80-90 • C [10] and/or after long exposure at room temperature (aging) [11]. For these reasons, they are mainly used for small non-structural components in many fields as such as automotive, hardware, electric/electronic devices, clothes, toys, sports, ornaments, etc. For instance, parts like safety belt blocks, locking mechanisms, wiper motor housings, cylinder locks, some electronic connectors, handles, tap systems, zippers, belt buckles, spring adjuster in bikes, costume jewelry, appliances, etc. are made from zinc-base alloys (Figure 1). Metals 2020, 1, x FOR PEER REVIEW 2 of 16fluidity, that helps in filling complex mold cavities and very thin sections, typically as low as 0.75 mm or even down to 0.13 mm [7]. They show good mechanical properties, including equivalent, or often better, bearing and wear properties than conventional Cu alloys [8,9]. Additionally, they offer good finishing and ability to be easily plated, making them more resistant to corrosion and wear and improving their aesthetic appearance. On the contrary, they suffer from reduction in performance above 80-90 °C [10] and/or after long e...