ZK60 + REE

Exploring the Tribological Behavior of ZK60 Magnesium Alloys with Rare Earth Element Additions

In the final year of my Master’s program, I had the chance to collaborate with the AMAs Research Group at MERC—a great opportunity that combined two areas I was already pretty familiar with: Contact Mechanics and FEM Simulation. The team needed someone who could bring both to the table, and thanks to my earlier work with Abaqus and coursework in Elasticity and Fatigue back in 2017, I was ready to jump in.

Over the course of four months, I dove deep into the subject. I spent a good chunk of time reviewing the literature and getting insights from researchers at MERC, K.N.Toosi University of Technology, and University of Tehran. This helped me quickly get up to speed and start contributing to the team’s ongoing research on ZK60 magnesium alloys—specifically, how adding rare earth (RE) elements like cerium (Ce) and yttrium (Y) impacts their microstructure and mechanical properties.

The Research Focus:

The goal was to improve the mechanical properties of ZK60 magnesium alloys by tweaking two things: the amount of RE elements (1, 2, and 3 wt.%) and the extrusion ratios used during processing (12:1 and 18:1). The team found that the best results came from adding 3 wt.% of either Ce or Y and using an 18:1 extrusion ratio—these combinations led to stronger and harder alloys. (You can read more about this in their earlier publication here.)

But there was still a gap when it came to understanding how these RE-modified alloys would behave in terms of friction and wear. That’s where I came in.

My Role:

To explore this open question, I ran a series of wear tests using a pin-on-disc (PoD) tribometer. I was mainly looking at friction coefficients, wear rates, and the dominant wear mechanisms, especially under different loads. This helped us see how the alloys performed under both mild and severe wear conditions.

To complement the lab work, I built a 3D finite element model in Abaqus, using a user-defined subroutine to simulate the contact pressure generated during sliding. With that data, I applied Archard’s wear equation to estimate wear depth for each alloy composition. Putting the experimental and simulation results side by side gave us a much fuller picture of how these alloys perform tribologically.

Summary of dominant wear mechanisms under different load regimes; Wear simulation procedure flowchart.

Outcomes and Publications:

The results were exciting: adding 3 wt.% of Ce and Y noticeably improved wear resistance, with Ce showing even stronger effects. Our FE model matched the experimental wear data with about 85% accuracy in mild wear, and around 75% in more severe conditions—which is quite solid.

Comparing experimental and simulation results of wear rate as a function of applied load for all studied alloys.

This project didn’t just teach me a lot—it also led to some meaningful outcomes. We presented our findings at the iMat2019 conference and published two peer-reviewed journal articles from the research (Banijamali et al., 2021), (Banijamali et al., 2022).

I also co-authored another paper on the work hardening behavior of the same alloys (Najafi et al., 2021).

Working on this project sharpened my skills in both experimental design and FE modeling, and deepened my understanding of tribology. Collaborating with the MERC team was a challenging and rewarding experience, and I’m proud to have contributed to advancing our knowledge of these high-performance magnesium alloys.

References

2022

MERC ZK #3
Experimental and Simulation Study on Wear Behavior of ZK60 Alloy with 3 wt.% Yttrium Addition

SM Banijamali, M Shariat Razavi, Y Palizdar, and 3 more authors

Journal of Materials Engineering and Performance, 2022

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In this study, the effect of 3 wt.% of Y addition on the wear behavior of ZK60 extruded alloy was investigated using both experiment and simulation. First, a pin-on-disc tribometer was used to test dry sliding wear against an AISI 52100 steel counterface in a load range of 5-60 N. Microstructural study revealed that adding Y to ZK60 alloy resulted in substantial grain refinement and formation of new precipitates. The wear rate and friction coefficient were reduced with Y addition, attributed to the formation of new precipitates and increased hardness. Increasing the normal load resulted in a transition from mild to severe wear. In the mild wear regime, abrasion was the dominant wear mechanism, while in the severe wear regime, oxidative wear and delamination (a sign of spallation of oxidized patches) coexisted with abrasion were dominant mechanisms. Finally, finite element method was employed to model the wear behavior of studied alloys using ABAQUS software. A 3D model was developed to predict the wear depth evaluated from contact pressure, which was then used as an input into Archard’s wear equation. In terms of wear rate, simulation results were in good agreement with experimental values, particularly in the mild wear regime.
@article{banijamali2022simulation, title = {Experimental and Simulation Study on Wear Behavior of ZK60 Alloy with 3 wt.\% Yttrium Addition}, author = {Banijamali, SM and Shariat Razavi, M and Palizdar, Y and Najafi, S and Sheikhani, A and Torkamani, H}, journal = {Journal of Materials Engineering and Performance}, volume = {31}, number = {6}, pages = {4721--4734}, year = {2022}, publisher = {Springer US}, doi = {10.1007/s11665-022-06585-y}, dimensions = {true}, }

2021

MERC ZK #1
Effect of Ce Addition on the Tribological Behavior of ZK60 Mg-Alloy

SM Banijamali, Y Palizdar, S Najafi, and 4 more authors

Metals and Materials International, 2021

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The present work aims to study the tribological behavior of an extruded ZK60 alloy in the presence of Ce; in a previous study, among ZK60 alloys with different Ce addition rates, an alloy with 3 wt% of Ce was found to exhibit the most promising mechanical (e.g., hardness and strengths) properties, while its wear behavior remained unknown. The results of microstructural examinations by optical and electron microscopes show that Ce addition reduces the grain size from 6.1 to 2.0 μm. Besides, in addition to the precipitates already distributed in the base alloy (Mg₇Zn₃), Ce could promote the formation of a new precipitate (MgZn₂Ce), increasing the total fraction of the precipitates. These microstructural evolutions enhance the strengths of the studied ZK60 alloy, as the yield and tensile strengths increase from 212 to 308 MPa and from 297 to 354 MPa, respectively. A pin on disc tribometer was employed to study the wear behavior of the developed alloy under different normal loads (5, 20, 40, and 60 N). The results show that the base and Ce-added alloys exhibit almost a similar frictional behavior, while the wear resistance of the Ce-added alloy is higher within the load ranges applied: (i) in low load conditions (5 and 20 N), where the abrasive wear is the active mechanism, the precipitates in the Ce-added alloy could enhance the wear resistance. (ii) Under the load of 40 N, oxidative wear is also an operative wear mechanism, leading to a sharp increase in the wear rate of the alloys. In this condition, Ce could provide a protective oxide layer, which could improve the wear resistance of the alloy. (iii) At a load of 60 N, both studied alloys exhibit a similar wear rate due to a severe oxidation condition. Therefore, beyond this loading condition, the microstructural evolutions (e.g., change in precipitation behavior) caused by Ce addition can no longer contribute to the enhancement of wear resistance.
@article{banijamali2021Ce, title = {Effect of Ce Addition on the Tribological Behavior of ZK60 Mg-Alloy}, author = {Banijamali, SM and Palizdar, Y and Najafi, S and Sheikhani, A and Soltan Ali Nezhad, M and Valizadeh Moghaddam, P and Torkamani, H}, journal = {Metals and Materials International}, volume = {27}, pages = {2732--2742}, year = {2021}, publisher = {The Korean Institute of Metals and Materials}, doi = {10.1007/s12540-020-00832-4}, dimensions = {true}, }
MERC ZK #2
The Effect of Y Addition on the Microstructure and Work Hardening Behavior of Mg-Zn-Zr Alloys

S Najafi, Y Palizdar, A Sheikhani, and 4 more authors

Journal of Materials Engineering and Performance, 2021

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The effect of adding different amounts of Y on the microstructure, mechanical properties, texture and work hardening behavior of the extruded Mg-6Zn-0.5Zr-xY alloys (x = 0, 1, 2, 3 wt.%) was investigated. According to the results, the microstructure of all alloys is composed of α-Mg grains and Mg₇Zn₃ particles. By adding Y, in addition to grain refinement, Mg₂₄Y₅ and Mg₃Y₂Zn₃ particles are formed in the microstructure. Among the alloys studied, the ZK60-3Y alloy has the highest strengths, as the yield stress and ultimate tensile strength of 318 and 366 MPa, respectively, were obtained for that alloy. This is due to the finer grains and higher volume fraction of the particles in the ZK60-3Y alloy. Meanwhile, reducing the grain size by Y addition affects the work hardening behavior; Y addition reduces the saturation stress, hardening capacity, and work hardening exponent by increasing the dynamic recovery; i.e., the more Y is added, the greater is the drop in the work hardening parameters. The effects of Y addition on work hardening behavior and dynamic recovery were investigated by examining microstructural developments, the volume fraction of particles and texture evaluation. The results of the texture evaluations showed that the addition of Y changes the texture component and intensity of the basal planes and can cause work hardening loss by activating slip on the non-basal planes.
@article{najafi2021WH, title = {The Effect of Y Addition on the Microstructure and Work Hardening Behavior of Mg-Zn-Zr Alloys}, author = {Najafi, S and Palizdar, Y and Sheikhani, A and Soltan Ali Nezhad, M and Abdiyan, F and Banijamali, SM and Torkamani, H}, journal = {Journal of Materials Engineering and Performance}, volume = {30}, pages = {2574--2585}, year = {2021}, publisher = {Springer US}, doi = {10.1007/s11665-021-05592-9}, dimensions = {true} }