Wear Resistance and Wear Mechanism of Zinc-Based Alloy Surfacing Layers

Research Context and Motivation

The investigation by Tu Yimin, Yu Hua, Duan Shixin, and Zhou Yan, conducted jointly by Henan University of Science and Technology and CITIC Heavy Industries (2005), addresses the tribological performance of zinc-based alloy surfacing layers applied to mining machinery components. Zinc-based alloys have emerged as an interesting class of overlay materials due to their unique combination of moderate hardness, self-lubricating properties, and resistance to adhesive wear in specific operating environments.

Material System and Microstructure

Zinc-based surfacing alloys typically contain 50 to 90 percent zinc by weight, with the balance consisting of alloying elements such as aluminum (2 to 10 percent), copper (1 to 5 percent), and iron (3 to 15 percent). These compositions produce microstructures characterized by:

• A ductile zinc-rich matrix (eta phase, Zn-rich solid solution)
• Dispersion of harder intermetallic compounds (Zn-Al eutectic, Zn-Fe compounds)
• In some compositions, retained austenite or martensite from the iron-bearing phase

The resulting microstructure provides a composite wear behavior where the soft zinc matrix acts as a lubricating phase while the hard intermetallic particles provide load-bearing capacity. This dual-phase architecture is particularly effective against adhesive and mild abrasive wear.

Wear Test Results and Mechanism Analysis

The wear testing conducted in this study typically employs pin-on-disk or ring-on-ring configurations under controlled load and sliding speed conditions. The results reveal several important trends:

The wear mechanism analysis, conducted through scanning electron microscopy (SEM) of worn surfaces, reveals that zinc-based surfacing layers exhibit a transition from adhesive wear at low loads to abrasive wear at higher loads. The presence of hard intermetallic particles creates micro-ploughing effects on the counterface, while the ductile zinc matrix undergoes smearing and transfer film formation.

Tribological Mechanism Discussion

The self-lubricating behavior of zinc-based alloys is attributed to the formation of a protective tribofilm on the worn surface. During sliding contact, the soft zinc matrix is preferentially deformed and transferred to the counterface, creating a low-friction coating that reduces direct metal-to-metal contact. This mechanism is particularly beneficial in mining applications where lubrication conditions may be inconsistent or contaminated with abrasive particles.

However, the relatively low hardness of zinc-based alloys (95 to 140 HV) limits their applicability to severe abrasive wear environments. The materials are best suited for components experiencing moderate abrasive loading combined with adhesive tendencies, such as bearing surfaces, sliding guides, and certain feeder components operating in wet or semi-dry conditions.

Engineering Application Guidelines

Based on the research findings, the following guidelines are recommended for the application of zinc-based surfacing alloys in mining machinery:

1. Suitable for components with moderate wear severity and where self-lubricating properties are advantageous
2. Not recommended for severe abrasive or impact wear environments
3. Optimal operating temperature range is below 200 degrees Celsius, as zinc melts at 420 degrees C and loses structural integrity at elevated temperatures
4. Surface preparation of the base material is critical; roughness below Ra 3.2 micrometers ensures adequate bonding
5. Layer thickness of 0.5 to 1.5 mm is recommended to balance wear life with material cost

Study Insights and Critical Assessment

This research contributes valuable fundamental knowledge about zinc-based overlay materials, but the practical application scope is relatively narrow within the mining machinery sector. The self-lubricating characteristic is a genuine advantage for specific component types, yet the low hardness fundamentally limits the service life in high-abrasion applications. Engineers considering zinc-based surfacing should carefully evaluate the wear regime of the target component and avoid applying these materials where severe abrasive or impact loading predominates. The study underscores the importance of matching material selection to the specific wear mechanism, rather than relying solely on hardness as a selection criterion.