METALLOGRAPHY OF SOLDERED LEAD AND LEAD ALLOYS - THE CASE OF EXTRUDEDALLOYS

The mixture of three parts acetic acid and one part hydrogen peroxide is probably the most widely used chemical polishing agent for lead and lead alloys. In certain conditions the structure is sufficiently reve aled that additional attack is not necessary. However, lead alloys are subject to structural changes (such as aging and recrystallization) a t room temperature. We have previously described a technique of electr olytic polishing at - 50-degrees-C followed by repeated chemical etchi ng with an appropriate reagent at 20-degrees-C. The applications of th is technique are various: observation of the not-yet-transformed struc ture, determination of the transformation sites (intercrystalline or i ntracrystalline), movement of transformation fronts along specific cry stallographic planes, measurement of the transformation front movement at different temperatures, and estimation of the transformed volume a nd of the activation energy associated with the transformation process . Classical soldering lines between two lead alloys of a different kin d or between two alloys of the same kind can also be observed using th is technique. However, the technique is not suitable in other cases, s uch as solderings obtained by extrusion. A new technique of deep disso lution has now been developed that allows us to reveal the soldered ex truded zones. It consists of chemical dissolution with a mixture of on e part acetic acid and three parts hydrogen peroxide.