Impression Creep Characteristics of a Cast Mg Alloy

Abstract

The creep behavior of the cast Mg-6Al-0.3Mn alloy (AM60) was investigated by impression testing under constant punching stress in the range 150 to 650 MPa and at temperatures in the range 423 to 523 K, corresponding to 0.458 < T/T m < 0.567. The creep behavior can be divided into two stress regimes, with a change from the low-stress regime to the high-stress regime occurring, depending on the testing temperature, around 0.021 < (r/G) < 0.033. Based on the steady-state power-law creep relationship, the stress exponents of 4 to 6 and 8 to 12 were obtained at low and high stresses, respectively. When the experimental creep rates were normalized to the pipe diffusion coefficient, however, the stress exponents of about 5 and 10 were obtained for the low-and high-stress regimes, respectively. The low-stress regime activation energies of about 76 to 84 kJ mol À1 , which are close to 80 kJ mol À1 for dislocation-pipe diffusion in the Mg, and stress exponents in the range 4 to 6 suggest that the operative creep mechanism is dislocation climb. This behavior is in contrast to the high-stress regime, in which the stress exponents of 8 to 12 and activation energies of about 134 to 165 kJ mol À1 are indicative of a power-law breakdown.

Effect of Ca and Rare Earth Elements on Impression Creep Properties of AZ91 Magnesium Alloy

“…The equivalent uniaxial creep strain rate (e ) and stress (r) can be evaluated from the impression velocity and impression stress, using the following two semiempirical relations: [31] r ¼ 4F…”

“…[35] Stress exponents higher than 6 have also been assigned to a power-law breakdown regime, characterized by an activation energy higher than that of the selfdiffusion energy. [29,31] For instance, values as large as 195 kJ/mol have been reported for the creep activation energy of Mg-Al-Ca alloy in the power-law breakdown regime. [29] The obtained activation energies in the present study are much lower than have been reported for the power-law breakdown regime.…”

Effects of Zr Additions on the Microstructure and Impression Creep Behavior of AZ91 Magnesium Alloy

“…The localized creep behavior of magnesium alloys has mostly been investigated by indentation tests using spherical indenters [20][21][22] and, in some more recent cases, by impression techniques. [23][24][25][26][27] The impression creep of Zr-containing Mg alloys has not been studied before, and thus, the aim of this study is to investigate the creep properties of this alloy using the impression testing technique.…”

Microstructure and impression creep characteristics Al-9Si-xCu aluminum alloys

“…Although impression creep technique has frequently been used for investigating creep properties of materials, it has not been standardized so far. It has been reported in many investigation that there is a good correspondence with results of both impression creep technique and those obtained from uniaxial tensile creep test [17,18]. Many investigations have been carried out on the impression creep properties of magnesium alloys, but impression creep properties of aluminum alloys have not been yet reported in the literature.…”