Effect of Homogenisation Parameters on Dissolution and Precipitation in Aluminium Alloy AA7150

Abstract

The thermal stability of constituent particles in both as-cast and homogenised alloy AA7150 has been investigated by means of scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). The results indicate that the as-cast eutectic starts to melt at 474°C and that the melting onset temperatures of the η- and S-phase particles after homogenisation are 474°C and 484°C, respectively. Two types of homogenisation treatments were used to dissolve eutectic particles: a two-step homogenisation treatment (40 h at 465°C + 4 h at 480°C) can completely dissolve the η- and S-based constituents, whereas a significant amount of S-phase still exists after a single-step homogenisation treatment of 40 h at 465°C. After utilising the two-step homogenisation treatment to dissolve all the η- and S-based constituents without overheating, samples were cooled at different controlled cooling rates and analysed by SEM and DSC to understand the effect of cooling rate on the type, size, distribution and density of precipitates formed during the cooling process. Slow cooling was found to result in the precipitation of coarse η-phase particles, with both the amounts and sizes of these η-phase particles increasing with decreasing cooling rate.

Solidification Paths and Phase Components at High Temperatures of High-Zn Al-Zn-Mg-Cu Alloys with Different Mg and Cu Contents

“…[17] Many investigations have been focused on the phase components of as-cast Al-Zn-Mg-Cu alloys so far, but different combinations of r, T, S, and h phases have been regarded as the phase components of the as-cast alloys (the impurity phases, e.g., Al 7 Cu 2 Fe and Mg 2 Si, are not considered here). [12,[18][19][20][21] For example, r and S phases were observed in the as-cast and homogenized 1973 Al alloy; [21] r, T, S, and possible h phases were found in a series of as-cast alloys within the AA 7055 Al alloy composition window. [20] Also, r, S, and h phases were observed in as-cast AA 7050 Al alloy, [12] but only r phase was found in as-cast AA 7150 and AA 7010 Al alloys.…”

“…[20] Also, r, S, and h phases were observed in as-cast AA 7050 Al alloy, [12] but only r phase was found in as-cast AA 7150 and AA 7010 Al alloys. [18,19] Therefore, how to judge or predict the phase components under designed alloy compositions should be very important with an urgent requirement, and indepth study of this point should be systematically and precisely performed.…”