METHOD FOR THE THERMAL TREATMENT OF FOUNDRY PIECES MADE FROM AN ALLOY BASED ON ALUMINIUM AND FOUNDRY PIECES WITH IMPROVED MECHANICAL PROPERTIES

摘要

Heat treatment of an aluminum-based alloy casting, especially one containing silicon, magnesium, and, if necessary, copper, comprises solution heat treatment over a first temperature range for a first time period; progressive cooling to a second temperature range lower than the first, continuing solution heat treatment in the second temperature range for a second time period, quenching and tempering. Preferred Features: The second temperature range is selected such that the treated alloy has tensile strength reduced by around 10-40%, preferably around 15-35%, with respect to the tensile strength that would be obtained with a single solution heat treatment process in the first temperature range and for a time period equal to that of the combined first and second time periods. The second temperature range is less than the first temperature range by about 8-14%. For a low-copper aluminum based alloy casting, the first temperature range is 510-550 degrees C, preferably 520-540 degrees C, the first time duration is 1-4 hours, preferably 1-2 hours, the second temperature range is 455-485 degrees C, preferably 460-480 degrees C, and the second time period is 1-5 hours, preferably 1-3 hours. The duration of the progressive cooling stage is greater than or equal to 30 minutes, preferably 1-2.5 hours. An Independent claim is given for an aluminum-based alloy casting, especially one containing silicon, magnesium, and, if necessary, Cu. The amount of copper is notably less than 1 weight %. The casting has tensile strength 220-300 MPa, elasticity limit at 0.2% deformation 170-270 MPa, and Brinell hardness 75-110.