Delayed fracture of aluminum alloys

Decomposition of the solid solution in commercial semiproducts from aluminum alloys

“…Analyzing the thermokinetic diagram of alloy 1420 [8] we established that in the region of low-temperature decomposition (the cts.~o I--~ 8"--> 8'-+ 8 phase transformation) v = 60 K/sec. This means that the hardening of commercial semiproducts from alloy 1420 is accompanied by a low-temperature decomposition of the solid solution.…”

“…Upon repeated long-term heating at low temperatures (technological or solar) we observe a phase transformation, i.e., GPB --> metastable S'-and 0'-phases. This causes a continuous decomposition of the solid solution and the appearance of anisotropy in the fracture resistance [8] of alloys D16T and l161T.…”

“…Later on, we established other characteristics more sensitive to the variation of Vcr, for example, the specific elongation in the heightwise direction of the semiproducts [9], the volume fraction of grain boundary fracture (GBF) [10], the fracture resistance H (the height of the "extrusion" zone determinable by analysis of fracture surfaces), and its anisotropy AH [8]. Using these characteristics we managed to discover the decomposition of the solid solution in the high-temperature region in continuous cooling at a cooling rate Vcool >> Vcr (for example, for alloy 1420 [9]), namely, vcr = 1 K/sec by the criterion of 98% % and vcr = 200 K/sec by the criterion of 95% 6, where 8 is the specific elongation over the height of the forging).…”

“…Using these characteristics we managed to discover the decomposition of the solid solution in the high-temperature region in continuous cooling at a cooling rate Vcool >> Vcr (for example, for alloy 1420 [9]), namely, vcr = 1 K/sec by the criterion of 98% % and vcr = 200 K/sec by the criterion of 95% 6, where 8 is the specific elongation over the height of the forging). Still earlier stages of the decomposition of the solid solution can be determined by evaluating Vcr with the help of the characteristics of crack resistance [8,10].…”

“…1). The shift of the C-diagram in the low-temperature range is caused by the strong supersaturation of the solid solution with lithium [8].…”