The advantage of using aluminum-lead alloys (Al-Pb) as a material for the manufacture of plain bearings is based on the fact that, besides being an excellent solid lubricant, Pb is abundant and has a low price. The problem encountered in preparing such alloys of lead contents ranging from 5 to 20 wt.% arises out of the low solubility of lead in aluminum at room temperature. To obtain complete solution of 8.5% lead in aluminum the alloy must be submitted to a temperature of at least 900.degree. C. Upon slow-cooling of an alloy of these elements, a complete precipitation and dissociation of the compounds takes place and, because of the great difference between their densities, causes a complete segregation of the lead which then rests on the bottom of the sample.
Notwithstanding this problem, the advantages offered by Al-Pb alloys gave rise to different methods aimed at the manufacture of bearing materials.
According to one of the prior art methods, the alloys, heated to the point of solubility of lead in aluminum, are rapidly atomized, to form a powder with the particles solidifying prior to segregation of the lead, the powder resulting from such atomization is collected and rolled to form a strip which is then bonded and laminated on a steel strip. The required rolling and lamination operations are complex and require sophisticated equipment.
According to another prior art method, the Al-Pb alloy, in dissolved state between the components, is cast directly on a steel strip. This method has several problems, among which are the segregation of lead during the relatively slow cooling and an extremely frail bonding.