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

PDF / 870,651 Bytes
10 Pages / 593.972 x 792 pts Page_size
15 Downloads / 261 Views

INTRODUCTION

MAGNESIUM alloys are particularly attractive for the aerospace and automotive industries due to their low densities.[1] AZ91 (Mg-9Al-0.8Zn-0.2Mn) alloy is the most common commercial magnesium alloy, which has the best combination of the mechanical properties and castability.[2,3] However, because of the rapid degradation of the mechanical properties, especially the creep properties at high temperatures, its application is limited to temperatures below 393 K (120 C).[4–6] Therefore, there have been various attempts to improve the hightemperature properties of AZ91 alloy by adding Ca, Sr, Sb, Bi, and rare earth (RE) elements.[7–17] The Ca is a relatively inexpensive element and its addition to Mg-Al base alloys can improve the maximum increase of both ambient and creep strength for the equal weight unit additions compared to Sr and RE elements.[18] An improvement in creep properties of AZ91 alloy has been reported by Amberger et al.[7] with the addition of Ca up to 5 wt pct. On the other hand, it has been shown that Ca, with the concentrations more than 1 wt pct, has a deleterious eﬀect on the room-temperature properties of AZ91 alloy.[13,19] The Ca also promotes the hot tearing susceptibility of AZ91 alloy.[19–22] Similarly, results of many studies have shown that RE elements up to about 2 wt pct can improve B. NAMI, Ph.D. Student, and H. RAZAVI, Assistant Professor, and S. MIRDAMADI and S.G. SHABESTARI, Professors, Center of Excellence for Advanced Materials and Processing (CEAMP), are with the School of Metallurgy and Materials Engineering, Iran University of Science and Technology (IUST), Narmak, Tehran, Iran. Contact e-mail: [email protected] S.M. MIRESMAEILI, Assistant Professor, is with the Department of Mechanical Engineering, Shahid Rajaee Teacher Training University (SRTTU), Lavizan, Tehran, Iran. Manuscript submitted September 13, 2009. Article published online May 22, 2010 METALLURGICAL AND MATERIALS TRANSACTIONS A

high-temperature mechanical properties of AZ91 alloy, whereas they show declines in corrosion resistance and room-temperature mechanical properties at concentrations over 1 wt pct.[9–13] Wang et al.[20] have reported that RE elements have little eﬀect on hot tearing susceptibility of AZ91 alloy up to about 1 wt pct. Also, it has been claimed that the ﬂuidity of AZ91 alloy is increased by adding RE elements.[21] The results in the literature have shown that the additions of Ca combined with RE to AZ91 alloy are more eﬀective in the improvement of its mechanical properties at room temperature.[13] However, there have not been many investigations in the literature concerning the simultaneous eﬀects of Ca and RE elements on the high-temperature mechanical properties of AZ91 alloy. In the present study, the eﬀects of Ca and RE elements on the creep properties of AZ91 alloy were studied using the impression creep method.

II.

EXPERIMENTAL PROCEDURE

An ingot of AZ91 magnesium alloy was melted in a steel crucible under protection of an atmosphere of air +5 pct SO2 at 750 ± 1 C. The

Data Loading...