Age‐hardening in a commercial Mg‐based alloy

Abstract

Age-hardening phenomena induced by thermal and thermo-mechanical treatments in the commercial Mgbased alloy WE54 were studied by positron annihilation lifetime spectroscopy and Vickers microhardness. To this aim, samples were plastically deformed and subsequently aged at 250 °C for times ranging from 0 to 1000 hours. The results obtained are discussed in terms of the role of vacancies in the solute transport and therefore they contribute to the discussion on the vacancy-solute clusters (and/or intermediate precipitates) interactions during the precipitation sequence of the WE54. Besides, we show that cold work previous aging not only accelerates but increases the hardening response of the alloy.

Vacancy–solute interactions during ageing of a cold-worked Mg–RE-based alloy

“…An important microstructural factor influencing the nucleation and growth of the strengthening precipitate phases in these age-hardenable alloys is the nature of lattice defects. In the specific case of WE54, which is the alloy selected for study in the present work, it has been reported that cold work after solution treatment and water quench and before artificial ageing at 200 and at 250 C, can accelerate and enhance the age-hardening response [10,11]. This effect is clearly shown by the hardening curves reported in [11] and shown in Figure 1 of the present paper for the convenience of readers.…”

“…In the specific case of WE54, which is the alloy selected for study in the present work, it has been reported that cold work after solution treatment and water quench and before artificial ageing at 200 and at 250 C, can accelerate and enhance the age-hardening response [10,11]. This effect is clearly shown by the hardening curves reported in [11] and shown in Figure 1 of the present paper for the convenience of readers. The beneficial effect of cold work on age-hardening enhancement is also well known for aluminum-based alloys (e.g.…”

“…To gain a deeper understanding of the interplay between solute atoms and open volume defects (vacancies and vacancy-like defects located in disordered regions and at interfaces) in the WE54 alloy, positron annihilation lifetime spectroscopy has been used by Macchi et al [11]. The propensity of the positrons to be trapped by open volumes inside solids makes positron annihilation lifetime spectroscopy the most sensitive technique for observing vacancy-like defects and the evolution of their density during structural transformation of alloys (for further information on positron annihilation lifetime spectroscopy studies of metallic alloys, see [14]).…”

Advances in positron studies of age hardening in light alloys

“…After an initial work in 2003, the IFIMAT-LNESS collaboration has concentrated the attention on the commercial alloys WE43, WE54 (Mg-Y-Nd) and EV31(Mg-Gd-Nd). [13,20,21,24,25]. In the first of these studies [13] has been shown that the evolution of the positron lifetimes is strictly correlated with the changes in hardness, which are enhanced and accelerated by plastic deformation prior to heating at 250°C (see Figure 9).…”

“…[13,20,21,24,25]. In the first of these studies [13] has been shown that the evolution of the positron lifetimes is strictly correlated with the changes in hardness, which are enhanced and accelerated by plastic deformation prior to heating at 250°C (see Figure 9). Further analysis based on PALS and CDB measurements at liquid nitrogen temperature, which are in part reported in [24], have clarified some important points regarding the role of the vacancies in the formation of precipitates.…”