Studies were made on corrosion resistance of high aluminum zinc base alloys by electro-chemical method, particularly on the effects of aluminum content, copper addition, addition of small amounts of other elements, and heat treatment.
The results obtained by (1) RGY tests and (2) corrosion potential measuring method were summarized as follows:
(1) RGY tests
It was shown among Zn-Al binary alloys that the current for bath voltage of Zn-22%Al alloy was higher than those of other high aluminum content alloys. In the alloys containing aluminum of more than 22%, the current for bath voltage decreased with the increase of aluminum content.
The corrosion resistance of Zn-22%Al alloy was considerably improved by addition of copper of 15%; and the optimum content of copper would be 1%.
The above corrosion resistance was reduced to minimum when the alloy was heated at 350°C for 24hrs., and then, water-cooled.
The corrosion resistance of Zn-22%-Cu1% alloy was improved by addition of a small amount of Ti, but was deteriorated by addition of a small amount of Ni.
(2) Corrosion potential measuring method
Among Zn-Al binary alloys, the corrosion potential of Zn-22%Al alloy became less noble after it was dipped in the solution for 1hr. The corrosion potential was nobler with the increase of aluminum content.
The corrosion potential was slightly nobler by addition of copper to Zn-22%Al alloy. However, the improvement in corrosion resistance of Zn-22%Al-1%Cu alloy could not be attained by addition of small amounts of other elements such as Mn, Ti, Ni, Mg, Zr, and V.
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