Intergranular magnesium alloys

Intergranular S.C.C. of magnesium alloys has also been reported, attributed to a grain-boundary phase of Mgi7Ali2 that causes galvanic attack of the adjacent matrix [8]. 

Corrosion activity may develop because of some heterogeneity in the grain boundary structure. In aluminum-copper alloys, precipitation of AI2CU particles at the grain boundaries leaves the adjacent solid solution anodic and more prone to corrosion. With aluminum-magnesium alloys, the opposite situation occurs, since the precipitated phase Mg Als is less noble than the solid solution. Serious intergranular attack in these two alloys may however be avoided, provided that correct manufacturing and heat treatment conditions are observed. 

The fracture mode of stress-corrosion cracks in austenitic stainless steels can be transgranular, intergranular or a mixture of both. One of the earliest environments found to cause problems was solutions containing chlorides or other halides and the data due to Copson (Fig. 8.30) is very informative. The test solution for that data was magnesium chloride at 154°C the alloys contained 18-20alloy with a composition of approximately 18Cr-8Ni has the least resistance to cracking in this environment. 

Intergranular Corrosion in Al-Mg-Si Alloys This class of heat-treatable alloys can be made resistant to IGG when an ideal combination of magnesium and silicon are alloyed to result in an Mg2Si... 

Intergranular corrosion occurs in stainless steels and alloys based on nickel, aluminium, magnesium, copper and cast zinc. In the following sections we shall look at the three former groups in some detail. 

Intergranular corrosion can also occur in other metals and alloys in connection with grain boundary precipitation, for example, in aluminum magnesium (AlMg) 5 alloy, nickel chromium 30 iron (NiCr30Fe), or Ti, and in methanol with traces of water and HCl. Solution annealed austenitic chromium-nickel steels can suffer intergranular corrosion from strong oxidants such as chromium... 

An experimental magnesium-base alloy sheet containing 14 % lithium and 2 % aluminum was reported to have experienced intergranular layer attack similar to the exfoliation of 2duminum-copper alloys [8],... 

---