Enhanced fatigue crack propagation resistance in a superhigh strength Al–Zn–Mg–Cu alloy by modifying RRA treatment

Improved fatigue crack growth resistance by retrogression and re‐aging heat treatment in 7010 aluminum alloy

“…The DSC scan results performed on the RRA‐treated alloy are shown in Figure . The endothermic peak at 192.5°C corresponds to the dissolution of the η′ precipitates . The large η′ precipitates in the matrix are due to two reasons: one is due to the higher retrogression temperature.…”

“…This reduces the grain growth and inhibits recrystallization during heat treatment process. Therefore, the influence of grain refinement and grain growth on the FCGR behavior in RRA is expected to be negligible, a similar observation made by Xia et al…”

“…At near‐threshold regime of FCGR, the plastic zone size at the crack tip is small, indicating average slipping distance of dislocation to be small . The FCGR behavior in aluminum alloys, especially in near‐threshold regime, is observed to be influenced by shearable nature of precipitates.…”

“…The RRA alloy also exhibits homogeneous distribution of η′ (MgZn 2 ) matrix precipitates but of two different kinds, ie, (1) fine spherical shaped precipitates with diameter of about 4 to 5 nm which are shearable in nature 24 and, (2) slightly coarsened disc shaped precipitates ( Figure 2C) of size about 12 to 15 nm 15 which are generally non-shearable. 19,30 The dark-field TEM micrograph of Figure 2E is presented in Figure 2F, which is captured by using η (GBPs) reflection which illuminates few of the coarsened matrix precipitates (12-15 nm). This confirms that some of the matrix precipitates that are grown to larger size during retrogression are similar in nature to that of GBPs (ie, non-shearable).…”

“…The endothermic peak at 192.5°C corresponds to the dissolution of the η′ precipitates. 29,30 The large η′ precipitates in the matrix are due to two reasons: one is due to the higher retrogression temperature. It is well known that during retrogression the GP zones are completely dissolved and unstable η′ precipitates get partially dissolved in the matrix and the stable η′ get coarsened.…”