Influence of loading path and precipitates on indentation creep behavior of wrought Mg–6 wt% Al–1 wt% Zn magnesium alloy Pranjal Nautiyal a,b , Jayant Jain b , Arvind Agarwal c,n a Discipline of Mechanical Engineering, Indian Institute of Information Technology, Design & Manufacturing, Jabalpur, Madhya Pradesh 482005, India b Department of Applied Mechanics, Indian Institute of Technology, Delhi 110016, India c Department of Mechanical and Materials Engineering, Florida International University, Miami, FL 33174, USA article info Article history: Received 31 August 2015 Received in revised form 10 October 2015 Accepted 11 October 2015 Keywords: Creep AZ61 Indentation Loading path Precipitates abstract This study reports the effect of loading path and precipitates on indentation induced creep behavior of AZ61 magnesium alloy. Indentation creep tests were performed on solution-treated and peak-aged ex- truded AZ61 magnesium alloy, and Atomic Force Microscopy (AFM) investigations were carried out to study deformation mechanisms. Twinning is the dominant creep mechanism for indentation along the extrusion direction (ED) in solution-treated alloy. A combination of slip and twinning appears to be the prominent mechanisms for indentation creep perpendicular to ED. Creep flow is arrested for indentation perpendicular to ED, due to slip–twin interactions. Influence of precipitates on creep deformation was also studied. Aged specimen exhibited higher creep resistance than solution-treated specimen. Unlike solution-treated specimens, twinning was not observed in aged alloy. Creep in aged specimen was at- tributed to slip. & 2015 Elsevier B.V. All rights reserved. 1. Introduction Magnesium alloys have decent strength, despite their light weight, making them desirable for structural applications. Mg–Al based alloys are the most popular of the magnesium alloys be- cause they exhibit optimum mechanical properties at room tem- perature. 1 or 2 wt% Zn is added to this binary system to further increase the strength of the alloy, giving rise to AZ series of ternary Mg–Al–Zn alloys [1,2]. These AZ alloys are especially employed in automotive vehicles, because of their light weight. However, their application is limited to 120 °C because of the low melting Mg 17 Al 12 precipitate phase, which softens at elevated tempera- tures, causing deterioration of creep resistance of these alloys [3]. Usually, creep in metals is considered to be of engineering sig- nificance at temperatures exceeding 0.4 T m [4]. Therefore, most of the creep studies on Mg alloys have been conducted at elevated temperatures. Creep at room temperature, which is only  0.32 T m for Mg alloys, has not received much attention by researchers. However, Miller observed AZ91 to creep at room temperature, well below its yield strength, while investigating the stress corrosion cracking (SCC) in the alloy [5]. This observation is of tremendous importance as it highlights the significance of room temperature creep in Mg alloys, and necessitates thorough study of the same to avoid catastrophic failure of structural components where these alloys are employed. Subsequent to this observation, Miller in- vestigated creep behavior of die-cast AZ91 by tensile testing technique at room temperature, and invoked dislocation climb as the rate-controlling creep mechanism in the alloy [6]. However, climb is a diffusion-driven process and is more likely to dominate at high temperature. We suspect whether it can play significant role at room temperature. It should also be noted that this in- vestigation was carried out on weakly textured alloy where it is very difficult to specifically probe the significance of individual deformation mechanisms on the creep response. Alternatively, creep study on strongly textured alloy can help in establishing the role of individual slip and twin systems on creep. Apart from Miller’s study, there is one more report by Han and co-workers on room temperature creep behavior of Mg–Al–Ca based AC52 alloy [7]. Creep deformation in this alloy was attributed to dislocation and twinning controlled mechanisms. Apart from these two stu- dies, there is no other report on room temperature creep behavior of Mg alloys to the best of our knowledge. Although there are a couple of reports on indentation creep of “pure” Mg at ambient temperature [8,9], but room temperature creep in Mg “alloys” has not been studied in detail. This necessitates systematic investiga- tion of room temperature creep in commercially viable Mg alloys. This study has been undertaken with the same objective. In this study, room temperature creep behavior of AZ61 alloy has been investigated. A salient feature of Han et al. work mentioned above was that Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/msea Materials Science & Engineering A http://dx.doi.org/10.1016/j.msea.2015.10.040 0921-5093/& 2015 Elsevier B.V. All rights reserved. n Corresponding author. E-mail address: agarwala@fiu.edu (A. Agarwal). Materials Science & Engineering A 650 (2016) 183–189