THE SYSTEMS ALUMINUM-TIN AND ALUMINUM-LEAD-TIN

Abstract

The solubility of tin in aluminum, between 400° and 645 °C, has been determined by an isothermal method. The system Al–Pb–Sn has been investigated, isothermally, at 500° and 600 °C. The eutectic temperature and composition of this system have also been determined. The structure of the phases in completely solid alloys has been identified by photomicrography. The liquidus curves at 500° and 600 °C. are continuous, extending across the ternary diagram from the Al–Pb system to the Al–Sn system. On neither of the two isotherms does a two-liquid region occur, despite the fact that a well-defined two-liquid region exists at temperatures above 650 °C. This was found to be due to inaccuracy in the published diagram for the Al–Sn system and this led to the work mentioned above. The solubility of tin in aluminum is much less than it has been supposed and this causes the surface of solid aluminum to intrude into the solid diagram at an early stage, thus blocking out the two-liquid region. The ternary eutectic temperature is 183.0 °C. and the composition, 0.08 weight per cent Al, 38.1% Pb, and 61.7% Sn. In any alloy at room temperature, the solid phases are: primary aluminum, α-lead, and β-tin. Brinell Ball and Vickers Diamond Pyramid hardness tests show that the ternary eutectic alloy is the hardest of the system. When alloys approximating to the eutectic composition are used as solders, it has been found that the alloy of ternary eutectic composition has a greater shear strength than ordinary solder.