Papers by Keyword: AZ91 Alloy

Abstract: Mg-Al-Zn alloy, an Mg alloy having Al and Zn as the major constituents, is exceptionally lightweight and has potential to become an essential component of modern engineering applications and healthcare systems. This paper presents valuable insights to the friction stir processing (FSP) applied to Mg-Al-Zn alloy in dry conditions. FSP induced extreme plastic deformation in the metal alloy which causes substantial microstructural alterations. These changes were investigated using optical microscope. Microstructural evaluation of FSP-processed zone indicated that average grain diameter of the FSP-processed zone increased in proportion to tool rotating speed. This is attributed to the frictional zone's degree of plastic deformation. In alignment with results obtained from optical microscopy, morphological study conducted using scanning electron microscope (SEM) also demonstrated the synthesis of refined grains. In addition, the study includes evaluation of the FSP-processed alloy's micro-hardness and tensile characteristics in contrast to the base (unprocessed) alloy.

Abstract: The microstructure of AZ91 (Mg-Al) alloy is comprised of α-Mg and β-Mg₁₇Al₁₂ massive phase. The lower melting point associated with the β-Mg₁₇Al₁₂ phase results in poor creep resistance of the alloy. In the present study, the AZ91 alloy with the addition of calcium (Ca, 1wt%) and cerium (Ce, 1wt%) is cast, and their effect on the microstructure and creep behavior of AZ91 alloy have been investigated. Thermally stable phases such as Al₂Ca and Al₁₁Ce₃ are introduced in the AZ91 alloy through the addition of Ca and Ce elements. Energy dispersive spectroscopy (EDS) and x-ray diffraction analysis confirmed the presence of these intermetallic phases in the microstructure. Tensile creep tests on the as-cast samples were performed at 175^°C temperature under 50 MPa stress. The study shows that the creep resistance of AZ91 alloy is greatly improved with the presence of Al₂Ca and Al₁₁Ce₃ intermetallic phases because of their better thermal stability than β-Mg₁₇Al_12.

Abstract: In this study, AZ91 alloy was used as the base material and calcium and cerium were added as alloying elements. Microstructural analysis through optical microscope (OM) and field emission scanning electron microscope (FESEM) revealed that AZ91 base alloy contains α-Mg matrix and β-Mg₁₇Al₁₂ interdendritic network. The inclusion of individual calcium and cerium resulted in a more homogeneous distribution of the interdendritic network in the AZ91-1wt.% Ca and AZ91-1wt.% Ce alloy. The secondary phase (Mg₁₇Al₁₂) was refined in the microstructure as a result of Ca and Ce addition where Ce addition forms a new rod-like phase that is recognized as Al₁₁Ce₃ and Ca addition forms a skeleton like structure of Mg₁₇Al₁₂ and Al₂Ca. Due to the formation of new Al₂Ca and Al₁₁Ce₃ intermetallics, the volume fraction of β-Mg₁₇Al₁₂ was more suppressed with Ca and Ce alloy additions. The grain size determined from Electron Backscatter Diffraction (EBSD) maps indicate the reduction in average grain size with individual Ca and Ce additions. The addition of these elements was found to improve the hardness of AZ91 alloy. Overall, the results of this study demonstrate the potential for using Calcium and Cerium as alloying elements in AZ91 alloy to improve its mechanical properties by modifying its microstructure.

Abstract: AZ91 Mg alloy is one of the most suitable alloy of magnesium for automotive and aerospace applications. In this study, tribological evaluation of AZ91 Mg alloy is performed against Al6351 alloy under dry sliding condition. The load was kept constant for a range (0.05-0.2 m/s) of sliding velocities. This study can be seen as an initial attempt in the direction of employment of Mg alloy for a dynamic engine component. The experiments were conducted on the solution treated and peak aged AZ91 Mg alloy by making a tribo pair with Al6351 alloy on a pin on disc setup under dry condition. The AZ91 and Al6351 alloys were used as a pin and a disc (flat) materials, respectively. The samples were characterized using hardness tester, tribometer and SEM/EDS. The wear mechanisms were identified by analyzing the worn surfaces and wear debris using SEM.

Abstract: The effect of Ca and RE metal additions on the precipitation and microstructure of as-cast AZ91 alloy was systematically investigated. It was found that Ca and RE additions could result in phase and microstructure changes. The XRD pattern showed the crystallite phase of as-cast AZ91 alloys consists of α-Mg matrix and β-Mg₁₇Al₁₂, however, after adding 1.5wt. % Ca and 0.8wt. % RE (0.5wt. % Sm and 0.3wt. % La), peaks coincident with Al₂Ca, Al₂Sm and Al₁₁La₃ intermetallic compounds were found, suggesting the generation of relative precipitates. The SEM images indicated that in as-cast alloys, the Al₂Ca intermetallic compound was located at grain boundaries with a lamellar structure, and the Al₂Sm intermetallic compound was homogeneously distributed in the α-Mg matrix or near the grain boundaries with a polygonal structure, and the Al₁₁La₃ intermetallic compound was located at grain boundaries with a needlelike structure. These intermetallic compounds could reduce the amount of β-Mg₁₇Al₁₂ and refine the microstructure of as-cast AZ91 alloy.

Abstract: This article presents the effect of individual addition of Sb, Sn and Pb on the precipitation sequence at room as well as high temperature tensile properties of AZ91 alloy. The results show grain refinement, formation of Mg₃Sb₂ and Mg₂Sn phases when Sb and Sn are added to AZ91 alloy. Lamellar precipitate is significantly suppressed while Pb added. Improved room and high temperature tensile properties are observed in Sb and Sn addition. Maximum tensile properties are noticed with AZ91 alloy having 0.5 wt.% Sb addition.

Abstract: In this paper, the microstructure, texture and tensile properties of the magnesium alloys AZ91 and ZM21 extruded at 350°C to the ratio 25:1 are investigated. After extrusion, the mean grain size reduces from 400 µm to 30 µm in ZM21 alloy and from 350 µm to 40 µm in AZ91 alloy. Bulk texture analysis indicates the formation of characteristic extrusion texture in both the alloys. The occurrence of dynamic recrystallization, as revealed through necklace structure formation, and the precipitation of second phase (Mg₁₇Al₁₂) particles in the AZ91 alloy are observed.

Abstract: Series of AZ91 alloy samples are prepared by adding different levels of Mg-Zn-Y quasicrystal master alloy under normal casting condition. The microstructure and mechanical properties of these samples are investigated by using of XRD, SEM, EDS and tensile test. It is shown that morphology of β- Mg₁₇Al₁₂ phase changes from continuous nets to discontinuous nets or even to particles. As results of these changes, the mechanical properties of AZ91 alloys are significantly improved until the addition level passes 6%.

Abstract: Microstructural evolutions of AZ91 magnesium alloy, which applied to homogenizing annealing treatment, hot extrusion and ageing treatment respectively, are investigated in this paper. Results exhibit that the massive β-Mg17Al12 phase appearing in the initial structure dissolves to eliminate in α-Mg matrix mostly due to the homogenizing annealing treatment; dynamic recrystallization and consequent grain refinement occur during extrusion; banded structure, in which the β-Mg17Al12 phase precipitates parallel to the extrusion direction in α-Mg matrix, are observed in the ageing treated specimen. Furthermore, the effects of temperature, keeping time of homogenizing annealing treatment and ageing treatment, and the extrusion processing parameter on the microstructural evolution of this alloy are also discussed according to the experimental results in details. In addition, the various mechanisms of the morphology and quantity of α-Mg and β-Mg17Al12 phase are analyzed corresponded to the various states. As for the banded structure appearing in the ageing treated specimen, it can be attributed to the banded segregation which remained in the extruded one and resulted from the casting dendrite and subsequent extrusion.

Abstract: Ultrasonic vibration was introduced into the molten AZ91 alloy in this paper. The effects of ultrasound power (from 0 to 900W) on the microstructure and mechanical properties of AZ91 alloy were investigated. The results show that the microstructure, hardness and mechanical properties of the AZ91 alloy have been improved with the ultrasonic treatment. In this work, the mechanical properties of the alloy reached the peak value when the ultrasound power was 600W. Also, the mechanism of ultrasonic vibration in the AZ91 alloy was discussed.