The Effect of Changes in the Aging Temperature Combined with Deep Cryogenic Treatment on the Structure, Phase Composition, and Micromechanical Properties of the WE43 Magnesium Alloy

Abstract

This paper examines the optimal aging temperature of WE43 alloy that has undergone precipitation hardening in conjunction with deep cryogenic treatment. The microstructure and phase composition were investigated, a microanalysis of the chemical composition was performed, and instrumental indentation tests were performed to determine the parameters of the micro-mechanical properties of the alloy after different heat treatment variants. It has been proven that a decrease in the aging temperature from 250 °C to 225 °C and the introduction of a deep cryogenic treatment lead to favorable changes in the microstructure of the alloy (reduction in grain size, increase in the number, and change in the type of β-phase precipitates). The changes in the alloy structure achieved by lowering the aging temperature contribute to the improvement of the micromechanical properties of the test material. The most advantageous results were recorded for an alloy subjected to solution treatment and aged at 225 °C for 24 h with deep cryogenic treatment: a 30% increase in hardness, a 10% increase in Young’s modulus, an improvement in elastic properties, and increased resistance to deformation of the alloy were shown compared to the initial (as-received) state. Raising the aging temperature to 250 °C leads to a phenomenon known as alloy overaging for both alloys after classical precipitation hardening and after deep cryogenic treatment. The results indicate the significant effectiveness of the proposed heat treatment in improving the service life of the Mg-Y-Nd-Zr (WE43) alloy.

Improving the Tribological Properties of WE43 and WE54 Magnesium Alloys by Deep Cryogenic Treatment with Precipitation Hardening in Linear Reciprocating Motion

“…The most advantageous results are obtained if significant amounts of precipitates consisting of a finely dispersed β' phase appear in the structure [25]. Implementing a complex heat treatment in the form of a combination of precipitation hardening and deep cryogenic treatment considerably promotes this process, as shown in previous work on both alloys [14][15][16], which has a direct impact on tribological properties regardless of the material couple used. Wear on the balls (counter-specimens made of AISI316-L, ZrO 2 , Si 3 N 4 , and WC) was not recorded, among other reasons, due to the large difference in hardness of the materials tested compared to WE43 and WE54 magnesium alloys.…”

“…Changes in the structure of WE43 and WE54 alloys obtained by applying a complex heat treatment consisting of solution treatment, aging, and cryogenic treatment in liquid nitrogen (before and after aging) resulted in improved micromechanical and mechanical properties such as an increase in H IT hardness, E IT Young's modulus, and compressive strength-UCS (R c ). These studies have been described in more detail in articles [15,16]. The improvement of these properties, in turn, had a direct impact on the tribological wear tested in four different material couples.…”

“…The improvement of tribological properties as a result of the proposed complex heat treatment is mainly related to the modification of the microstructure of the alloys-the formation of a much larger amount of β' phase precipitates-Mg46.1Y6.25RE3.45 and the presence of other phases such as Mg41Nd5, La0.5RE, Mg3RE, Mg2Nd, MgRE, MgY, and Y0.65RE0.35 in the alloy subjected to sub-zero treatment in combination with additional heat treatment. These lamellar precipitates modify the mechanical, micromechanical, and sclerometric properties of the alloy [16,23], leading to an improvement in the service life of both alloys, which is directly evident through a significant improvement in tribological properties and a reduction in wear. The solution treatment of WE43 and WE54 alloys results in the dissolution of intermetallic phases in the solid solution matrix and an increase in the average grain area of the α-Mg solid solution [22].…”

“…The process of precipitation hardening was conducted in the FCF-5M laboratory muffle furnace (Czylok, Jastrzębie-Zdrój, Poland) in the air atmosphere. The temperature of solution treatment, aging, and heat treatment have been determined in previous studies [14][15][16]. For both alloys, the solution treatment (Sol) temperature was 545 • C and the solution treatment time was 8 h. The aging (Age) temperature for WE43 alloy was 225 • C and 250 • C for WE54 alloy.…”

“…Magnesium and magnesium alloys are characterized by excellent biocompatibility, good mechanical strength, and biodegradation properties. The modulus of elasticity of magnesium is approximately 45 GPa, which is of the same order of magnitude as that of bones (15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25), resulting in reduced stress shielding. The density of Mg alloys ranges from 1.74 to 1.84 g/cm 3 , depending on the alloy components, and is nearly equal to that of bone (1.8-2.1 g/cm 3 ).…”