Graphical abstract The conglomeration states of the dust particles had a great effect on the initial atmospheric corrosion behaviour of the AM60 Mg alloy. The larger pit like one in site A was caused by the conglomeration of many dust particles with rough surfaces, whereas the smaller pit like one in site B resulted from the unconglomerated particles or single ones with smoother surfaces. Consequently, the pit sizes were relative to the conglomerate states of the particles on the alloy. Highlights ► Atmospheric corrosion behaviour of AM60 Mg alloys was studied. ► The sizes of dust particle conglomerates were related to the sizes of pits. ► Corrosion rate of the ingot was higher than that of the extruded samples. ► The main corrosion products of both alloys were MgSO4·6H2O and MgSO3·6H2O. ► The extruded alloy with uniform microstructures showed a lower corrosion rate.