Indentation creep behavior of AZ61-0.7Si-xCa magnesium alloys

Subject Areas : journal of New Materials

Nikoo Berenji Tehrahi ¹ (Department of metallurgy and materials engineering, South Tehran Branch, Islamic Azad University, Tehran ,Iran)
Reza Mahmudi ² (School of Metallurgical and Materials Engineering, College of Engineering, University of Tehran, Tehran, Iran)
Abdolreza Geranmayeh ³ (Department of Mechanical Engineering, South Tehran Branch, Islamic Azad University, Tehran ,Iran)

Received: 2018-02-05 Accepted : 2018-12-15 Published : 2019-04-21

Keywords: AZ61‒0.7Si alloy, Creep mechanism, Indentation creep, Mg2Si morphology,

Abstract :

The effect of 0.2, 0.5 and 1.0 wt% Ca additions on the microstructure and creep behavior of an Mg‒6Al‒1Zn‒0.7Si cast alloy was investigated by indentation creep test under constant loads of 5 and 15 N and at temperatures in the range of 448–523 K. The microstructural examination of alloys was conducted using electron microscopy (SEM), and X‒ray diffraction (XRD). Results showed that addition of Ca enhances hardness and the thermal stability of the alloys. It was found that AZ61‒0.7Si‒1.0Ca had the best creep resistance among three tested alloys. The main cause of enhancing mechanical properties of Ca-containing alloys was the change in the morphology of Mg2Si phase from Chinese script to polygonal shape, with formation of CaSi2 and CaMgSi phases. Stress exponents of all alloys showed two different regimes in creep tests. In the low stress regime, n-values of about 4–7 and activation energies of about 95 kJ/mol, introduce pipe-diffusion-controlled dislocation viscous glide as the controlling creep mechanism. In the high stress regime, however, stress exponents of about 11–14 and activation energies of about 135 kJ/mol, suggest that deformation mechanism is dislocation climb with some sort of back stress, similar to those noted in dispersion strengthening alloys.

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