The effect of Y and Nd additions on the microstructure and creep behavior of AZ80

The effect of yttrium (0.2Y wt.%) and yttrium + neodyminum (0.1Y+0.1Nd wt.%) additions on the long-term (>1200 h) tensile creep and microstructural evolution of AZ80 was investigated at temperatures ranging between 100 °C and 150 °C and stresses ranging between 50 MPa and 100 MPa. The alloying resulted in both the formation of Y- and/or Nd containing particles, and lower tensile strengths and elongation-to-failure. The minimum creep rate (ε˙min) increased with increasing applied creep temperature and stress. Y addition resulted in greater creep-resistance compared with that for (Y + Nd) additions. The ε˙min of AZ80 + 0.2Y was approximately half that of AZ80 at 50 MPa at 150 °C. The apparent creep activation energy for each alloy ranged between 73 and 93 kJ/mol, and pipe-diffusion-assisted dislocation creep was suggested to be the dominant secondary stage creep deformation mechanism. Discontinuous precipitation (DP) occurred during the creep exposure but was impeded by precipitate-containing twins. The DP was less concentrated in the Y and (Y + Nd) containing alloys, which exhibited lower Vickers hardness values than AZ80. Grain boundary and twin boundary cavitation/cracking were prevalent during creep. Minor Y or (Y + Nd) addition, resulted in less oxidation and extended the intermediate-temperature creep life. •Minor Y or (Y + Nd) additions improved the intermediate-temperature creep resistance of annealed AZ80.•Minor Y or (Y + Nd) additions suppressed the oxidation of AZ80 and extended the intermediate-temperature creep life.•Twin plays an important role in the intermediate-temperature creep deformation of AZ80 with Y and/or (Y + Nd) additions.•Discontinuous precipitation was impeded by the twin rich in precipitation.