Weathering of Casting Alloys

It has been known for more than 50 years that sihcon- and magnesium-containing casting alloys have an excellent resistance to atmospheric corrosion. The first testing results over 10 years in industrial atmosphere in the United States, published in 1946, showed that the pitting depth of samples of A-S5 (5% silicon) and A-S12 (alloy 44100, containing 1% iron) does not exceed 175 p.m [14]. These results were confirmed by subsequent tests, also in industrial atmosphere over 13 years, that showed that the pitting depth does not exceed 200 p,m on the alloys A-S13 (alloy 44100) and A-G5 (alloy 51300) [15]. 

In general, casting alloys without copper of the 40000 and 50000 series show an excellent resistance to atmospheric corrosion. They are widely used in construction and ship building (the upperworks of small crafts is made of anodised A-3GT (51100) and A-G6 (51300)), electrical engineering, etc. 

The use of copper-containing alloys of the 20000 series and of alloys of the 40000 series A-S12U (47000), A-S7U3 (46200) and A-S9U3 (46400) should be avoided. From experience we know that severe corrosion can occur in urban and industrial atmospheres. Rupture of load-bearing pieces made of the A-U5GT alloy (43500) has been observed in aggressive atmospheres. 

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