Bond criterion in cold pressure welding of aluminium

Abstract

An experimental apparatus to examine a bond criterion is developed. Using this apparatus, it is possible to carry out lap welding using punches that penetrate into strips of the experimental metal; these strips are simultaneously extended in the direction parallel to the bonding surface by bulging. The bond strength is investigated by varying independently the virgin surface ratio α and the normal bonding pressure p. The bond efficiency η, i.e. the ratio of the bond strength to the strength of the base metal, increases with values of α and p. However, when p has a value of 75 MN m−2 the value of η is always 0% at any value of α. It is possible to commence bonding when p=112 MN m−2, a value that is nearly equal to the flow stress of the base metal Y, i.e. p/Y ≍ 1. When p > 225 MN m−2, i.e. p/Y ≥ 2, the value of η does not depend on p, but on α, i.e. bonding commences when α =20% and the value of η reaches 100% when α=55–60%. This means that it is possible to achieve efficient bonding when the value of p is about twice the flow stress of the base metal, i.e. p/Y ≥ 2.MST/889