The effect of Ca and RE elements on the precipitation kinetics of Mg17Al12 phase during artificial aging of magnesium alloy AZ91

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Vol. 528; no. 15; pp. 5018 - 5024
• Main Authors: AMIR ESGANDARI, B, MEHRJOO, H, NAMI, B, MIRESMAEILI, S. M
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier 15.06.2011
• Subjects: Applied sciences; Creep; Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Hardness; Materials science; Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology; Metals. Metallurgy; Phase diagrams and microstructures developed by solidification and solid-solid phase transformations; Physics; Precipitation; Creep; Calcium; Creep strength; Aluminium alloy; Hardness; Precipitation hardening; AZ91 magnesium alloy; Dislocation; Grain boundary; Rare-earth metal addition; Phase transformation; Magnesium base alloys; Precipitation; Rare earth elements; Calcium addition; Artificial ageing; Kinetics; Age hardening
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/j.msea.2011.03.022

Highlights ao Ca and RE elements decrease the precipitation rate during aging of AZ91 alloy. ao Precipitation kinetics and mechanism during aging of the alloys were studied. ao Effect of Ca and RE on creep properties of age hardened AZ91 alloy was studied. The effect of simultaneous alloying with Ca and rare earth (RE) elements on the age hardening kinetics of AZ91 was studied through the fitting of the JohnsonaMehlaAvrami (JMA) equation. The results showed that the addition of both Ca and RE elements not only suppress discontinuous precipitation of the Mg17Al12 phase during the age hardening process, but also decrease the alloy hardness. Fitting the JMA equation to the experimental data indicated that the phase transformation during age hardening of an alloy variant containing both Ca and RE (at 170ADGC and 190ADGC) and standard AZ91 (at 170ADGC) takes place by the nucleation of precipitates on dislocations. In contrast, the precipitation during age hardening of AZ91 at 190ADGC occurs via nucleation at grain boundaries. Although it was observed that the creep strength of age hardened specimens are lower than that of the as cast specimens, but age hardening treatment has lower deleterious influence on the creep resistance of the alloy containing Ca and RE in comparison with conventional AZ91. This may be ascribed to the decreased precipitation rate resulting from the addition of both Ca and RE elements.