Discussion on "Recent developments in light alloy pistons" at the Coventry Section of the Institution

Mr. Lewis: I am sure it is very interesting to hear what Mr. Mabrey has had to say about the use and development of silicon alloy. He mentioned a silicon alloy that can be hardened by heat treatment 140-150. What other elements are introduced in the alloy to bring about this hardening effect? Mr. Mabrey stressed what those of us who have had practical experience of pistons know¿if you start a piston with a Brinell of 140, by continual service this figure does drop almost to the " as cast " condition. I would like to put the case that if you take an alloy " as cast " you do not subject it to any heat treatment at all; if you heat that silicon alloy and cool it, you will again get a drop in the original Brinell " as cast." If you would like to graph the drop, taking from the bar " as cast " you will find that they follow each other fairly faithfully. The higher Brinell figures will drop more rapidly than the " as cast " but if you heat them and cool them as many as a hundred times you will find there is still a difference.