HARDENSS TESTING

The Vickers Hardness Test on anodic coatings is carried out on the edge of the film so that the effect of the underlying, soft, aluminium is eliminated. This requires a section of the sample to be made, which is then suitably mounted (usually in a resin) and subsequently polished. The prepared sample is then put on the tester's table and the operator uses it's microscope to find the anodic film. Once a target area is found the test can begin. This uses a pyramid shaped diamond tip, which bears on the target under a given load. The operator then measures the width of the resulting indentation. With the above machine one simply puts markers at each extreme of the indentation, the machine does the rest, calculating the relationship between the applied load and the size of the indentation to give a number, usually with hard anodising in the range 350-550. To get a very rough comparison with Rockwell 'C' just divide this number by twelve.

We would argue that this method of testing tells one how crushable the anodic coating is which does not give an accurate indication of wear resistance. For example, both hard chrome and electroless nickel plating can have Vickers hardness readings up to one thousand, but inferior wear resistance to hard anodising with a Vickers number of less than 500.

HARDNESS COMPARISON