Effects of Gd, Y, and La Rare-Earth Elements on the Microstructural Stability and Elevated-Temperature Mechanical Proper
- PDF / 5,667,295 Bytes
- 12 Pages / 593.972 x 792 pts Page_size
- 18 Downloads / 269 Views
ON
AMONG various Mg alloys, the Mg-Al-Zn series, designated as AZ alloys, exhibit appropriate mechanical properties and corrosion resistance.[1–3] These alloys possess interesting characteristics including low-specific gravity, high-specific strength and stiffness, and excellent machinability. Due to such admiring properties, these alloys have found practical uses in automotive industries. One of the most important shortcomings in the application of these alloys, however, is their pronounced softening, and thus, relatively low strength and creep resistance at high working temperatures. Therefore, designing Mg-based alloys with high-thermal stability at
SEYED MASOUD ASHRAFIZADEH and REZA MAHMUDI are with the School of Metallurgical and Materials Engineering, College of Engineering, University of Tehran, Tehran, Iran. Contact e-mail: [email protected] Manuscript submitted March 10, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS A
elevated temperatures has attracted the attention of several researchers in this field.[4,5] One of the feasible means of overcoming the above-mentioned deficiency is the incorporation of some alloying elements that can form thermally stable second-phase particles.[6–11] Accordingly, a notable progress has occurred by the introduction of different rare-earth (RE) elements into the Mg matrix. Gadolinium (Gd) is a RE element that has recently gained a prevalent interest as an alloying element in the Mg alloys.[12] The influence of various contents of Gd on the microstructure of cast Mg has been examined. The results have shown improvements in strength values due to the formation of MgGd and Mg5Gd particles.[13] In a separate research, the addition of 1 to 4 wt pct of Gd to an AZ21 Mg alloy has been considered. The results revealed the formation of both (Mg, Al)3Gd phase with branch-shaped morphology as well as Al2Gd particles with cubic shape morphology; both of which resulted in some improvements in tensile strength and creep resistance.[14] Minor addition of Gd to AZ80 alloy has indicated that in the AZ80 + 1Gd alloy, the partially agglomerated particles were mainly
Al2Gd.[15] In addition to particle hardening, Gd is known to strengthen the Mg matrix via solid solution hardening.[16] Another aspect of Gd addition to Mg-Al alloys is its grain refinement capability.[17,18] In several researches, the effect of Y addition on the microstructure and properties of the Mg-Al-Zn alloys has been investigated. It has been reported that through addition of Y, the morphology of b-Mg17Al12 phase changes and the new reinforcing phase of Al2Y with a face center cubic (FCC) structure and cuboid morphology is formed in the a-Mg matrix. The formation of the stable Al2Y phase, with a melting point of 1536 °C, has been introduced as the main cause of improved hardness and corrosion resistance,[19–23] tensile strength,[24] and creep resistance.[25] The most common RE elements that are used to improve the high-temperature mechanical properties of the AZ magnesium alloys are lanthanum (La) and cerium (Ce).[26,27] Mahmudi
Data Loading...
