The Sclerometrical, Mechanical, and Wear Behavior of Mg-Y-Nd Magnesium Alloy after Deep Cryogenic Treatment Combined with Heat Treatment

Abstract

The paper investigates changes in the structure, microhardness, and sclerometrical and tribological properties of a Mg-Y-Nd alloy under the influence of deep cryogenic treatment (DCT) in combination with heat treatment. The solution treatment was carried out at 545 °C for 8 h, aging was carried out at 250 °C for 24 h, and the deep cryogenic treatment applied at different treatment stages was performed at −196 °C. Tests showed a significant increase in the number of β-phase precipitates identified as Mg46.1Y6.25RE3.45 in the alloy subjected to DCT after solution treatment followed by aging. In addition, an approximately 20% reduction of the grain size was observed. Changes in the structure in the precipitation process strengthened the alloy and resulted in an increase of its hardness. At the same time, sclerometric tests allowed the micromechanism of wear and the coefficient of resistance to abrasive wear to be determined. Tribological tests showed a three-fold reduction in the volumetric wear and a considerable reduction of the friction coefficient, with the main mechanism observed during friction being abrasive wear. The most favorable properties of the alloy were obtained after precipitation hardening combined with DCT, resulting in a large increase in resistance to abrasive wear. Additionally, the formation of deep scratches in the examined material was reduced. The introduction of sub-zero treatment reduces the precipitation hardening time, and the results obtained indicate that the service life of the Mg-Y-Nd alloy can be extended.

Investigation of Micromechanical Properties and Tribological Behavior of WE43 Magnesium Alloy after Deep Cryogenic Treatment Combined with Precipitation Hardening

“…The above results corroborate that increasing the amount of β -phase lamellar precipitates by introducing deep cryogenic treatment to the precipitation hardening process effectively reduces the tribological wear of the investigated alloy. Similar observations can be found in the literature in works on magnesium alloys with aluminium [ 16 , 21 ] and gadolinium [ 22 , 23 , 24 , 25 , 26 ] additions, and in our previous papers concerning WE54 magnesium alloy [ 27 , 28 ].…”

“…The sub-zero treatment alone, in turn, resulted in an approximate 5–8% increase in micromechanical properties. The observed effects are the result of changes in the structure of the Mg-Y-Nd alloy studied by the authors in previous articles [ 27 , 28 ], where it was shown that deep cryogenic treatment caused a twofold increase in the number of β -phase precipitates and decrease in the grain area compared to the alloy aged without sub-zero treatment. The large number of additional precipitates formed as a result of deep cryogenic treatment after solution treatment can be explained by the formation of additional nucleation sites in magnesium alloys [ 15 ], which also occurs, among others, in magnesium alloys with aluminum and with gadolinium [ 20 , 21 , 22 , 23 , 24 , 25 , 26 , 33 , 34 ].…”

“…Solutioning and aging were carried out in a laboratory muffle furnace, FCF-5M (Czylok, Jastrzębie-Zdrój, Poland), in the air atmosphere. The time and temperature of solutioning were set at 8 h and 545 °C during the previous tests, while the aging time was set at 24 h at 250 °C [ 14 , 27 , 28 ]. Five different variants of the state of the test material were obtained: as-delivered alloy, after deep cryogenic treatment (DCT), after solutioning and subsequent deep cryogenic treatment (S + DCT), and after precipitation hardening without (S + A) and with deep cryogenic treatment (S + DCT + A + DCT).…”

“…Wear tests in rotational motion were carried out on a TRN tribological tester (Anton Paar, Corcelles-Cormondrèche, Switzerland) in the ball-on-disc system ( Figure 2 ). Test parameters were set based on previous studies [ 14 , 27 , 28 ] and the recommendations of the ASTM G99 standard [ 32 ]. The tests were performed in the following conditions: Load— F n : 10 (N) Friction distance radius— r : 7 (mm) Linear velocity— v : 0.15 (m/s) Distance— s : 100 (m) Ambient temperature: 21 ± 1 (°C) Air humidity: 40% ± 5 (%) …”

“…This applies in particular to magnesium alloys with rare earth elements. The few exceptions are two earlier papers by the authors about the WE54 alloy [ 27 , 28 ]. The aim of the present study was to determine the changes in micromechanical properties and tribological behavior induced by the proposed treatment.…”