Wear Resistance and Wear Mechanism of Zinc-Based Alloy Weld Overlay Layers

Literature Overview

This research by Tu Yimin, Yu Hua, Duan Shixin, and Zhou Yan from Henan University of Science and Technology and CITIC Heavy Industries Co., Ltd. (2005) investigates the tribological performance and wear mechanisms of zinc-based alloy weld overlay coatings applied to mining machinery components. The study addresses a critical materials selection challenge: balancing corrosion resistance (provided by zinc) with wear resistance (required for mining applications) in a single overlay layer.

Background and Motivation

Zinc-based alloys, including zinc-aluminum alloys and zinc-magnesium alloys, are widely used for corrosion protection in marine and atmospheric environments due to their sacrificial anodic properties. However, zinc's inherently low hardness (approximately 50–80 HV for pure zinc) renders it unsuitable for abrasive wear environments without modification. Mining machinery components frequently operate in dual-service conditions — exposed to corrosive moisture while subjected to abrasive particle impact — creating a demand for overlay materials that combine both properties.

Zinc-Based Alloy Compositions Studied

Wear Mechanism Analysis

Primary Wear Mechanisms Identified

1. Abrasive wear (dominant): Hard particles in the mining environment (quartz, feldspar, hematite) embed into the softer zinc matrix and plough through the surface, creating grooves and material removal. The wear rate is governed by the Archard equation modified for composite materials, where the relative hardness ratio between the abrasive particle and the overlay determines the wear mechanism transition from micro-ploughing to micro-cutting.
2. Adhesive wear (secondary): Under high contact pressure, zinc's ductility promotes material transfer to the counterface. This mechanism becomes significant when the overlay encounters steel counterfaces under heavy loading conditions.
3. Fatigue wear (tertiary): Cyclic loading causes micro-crack initiation at the overlay-bond line or within the overlay layer, leading to spalling. The fatigue life is particularly sensitive to the quality of the metallurgical bond between the zinc-based overlay and the steel substrate.

Microstructural Contributions to Wear Performance

The wear resistance of zinc-based overlays is governed by several microstructural features:

• Aluminum-rich phases (Zn₅Al₈, Al₂ZnMg): These intermetallic phases provide the primary wear resistance contribution, with hardness values of 150–250 HV. Their volume fraction and distribution uniformity directly affect wear life.
• Magnesium-containing phases (Zn₄₃Mg₃₂Al₉): These phases improve adhesion to the steel substrate and contribute to crack resistance.
• Eutectic microstructure: The Zn-Al eutectic (at approximately 22 wt% Al) provides a fine, uniform microstructure that resists crack propagation.

Process Parameters Affecting Wear Performance

Dilution Control and Its Impact

Dilution is the most critical process variable for zinc-based overlays because zinc's low melting point (420°C) compared to steel (1500°C) creates a significant challenge. Excessive dilution (> 25%) introduces iron into the overlay, reducing the corrosion protection effectiveness while potentially increasing hardness. The target dilution for optimal performance is typically 10–20%, which can be achieved through:

• Using a high-current, short-arc process (e.g., hot-wire TIG or GMAW with high current density)
• Applying a soft solder or brazing transition layer between the base metal and overlay
• Using a low-heat-input process with thin, closely-spaced beads
• Preheating the base metal to reduce thermal gradient

Engineering Practice and Case Studies

In mining applications, zinc-based overlays have been successfully applied to:

• Conveyor belt transition sections: Where the belt passes over pulleys, zinc overlays provide corrosion protection against moisture while the aluminum-rich phases resist light abrasion from belt material.
• Slurry pump impellers: The combination of corrosion resistance and moderate wear resistance extends service life by 2–3 times compared to unprotected carbon steel.
• Mining truck chassis components: Exposed to road salt and abrasive dust, zinc-based overlays provide dual protection.

Defect Analysis and Quality Control

Study Insights and Implications

The research by Tu Yimin and colleagues established that zinc-based alloy overlays can achieve acceptable wear performance in mining applications when the alloy composition is properly designed to maximize the volume fraction of hard intermetallic phases. The key insight is that wear resistance in zinc-based systems is not achieved by increasing the hardness of the zinc matrix itself (which is thermodynamically limited) but by engineering a composite microstructure with dispersed hard phases.

The practical implication for engineers is that zinc-based overlays should not be considered as direct substitutes for conventional hardfacing alloys in severe abrasive wear applications. Rather, they serve a niche role where corrosion protection is the primary requirement and wear conditions are moderate. For severe abrasive wear, traditional Fe-Cr-C or Co-Cr hardfacing alloys remain the preferred choice, while zinc-based overlays are best deployed in dual-service environments where corrosion protection is equally or more important than wear resistance.

The wear mechanism analysis conducted in this study provides a framework for predicting overlay performance in specific mining environments. By characterizing the dominant wear mechanism (abrasive, adhesive, or fatigue) for a given application, engineers can select the appropriate zinc alloy composition and process parameters to optimize service life.