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

Literature Overview and Research Background

The study of zinc-based alloy weld overlay layers addresses a critical engineering challenge in the protection of structural components subjected to severe abrasive and erosive environments. Zinc-based alloys, including Zn-Al and Zn-Cu systems, have traditionally been valued for their corrosion resistance in galvanizing applications, yet their potential as wear-resistant overlay coatings has remained underexplored. This literature review examines the microstructural evolution, mechanical properties, and wear mechanisms of zinc-based alloy cladding layers produced through various welding processes. The research is particularly relevant to engineers working on hydraulic equipment, mining machinery, and chemical processing vessels where zinc-based overlays may serve as sacrificial or protective layers against erosion-corrosion.

The fundamental motivation behind this research stems from the observation that conventional zinc coatings applied by hot-dip or spray methods often suffer from insufficient bond strength and limited thickness. Weld overlay techniques, by contrast, can produce thicker, metallurgically bonded layers with improved durability. The study systematically investigates how alloy composition, welding parameters, and heat treatment affect the hardness profile, microstructure, and wear behavior of zinc-based overlay deposits.

Core Technical Content and Key Findings

The research employs metallographic analysis, X-ray diffraction, scanning electron microscopy, and pin-on-disk wear testing to characterize the overlay layers. The primary finding is that the addition of aluminum to the zinc matrix significantly enhances hardness through solid solution strengthening and the formation of intermetallic compounds such as Zn-Al phases. The hardness of pure zinc overlay deposits typically ranges from 40 to 60 HV, while Zn-Al alloys with 5 to 15 wt% aluminum can achieve hardness values of 80 to 120 HV.

The wear mechanism analysis reveals a transition from adhesive wear in pure zinc to predominantly abrasive wear in zinc-aluminum alloys. The presence of hard intermetallic phases acts as a barrier to material removal, while the softer zinc matrix provides ductility that prevents catastrophic spalling. Under dry sliding conditions, the Zn-10Al alloy demonstrated the optimal balance between hardness and toughness, exhibiting a specific wear rate approximately 75% lower than the base zinc coating.

Microstructural Analysis and Wear Mechanism Interpretation

The microstructure of the zinc-based overlay layers consists of a dendritic solidification pattern with interdendritic regions enriched in aluminum. The primary dendrite arms are composed of FCC zinc solid solution, while the interdendritic zones contain hexagonal Zn-Al intermetallic compounds. This hierarchical microstructure is critical to the wear resistance, as the hard phases resist plowing and cutting by abrasive particles, while the ductile matrix accommodates plastic deformation without cracking.

Fractography of the worn surfaces reveals that material removal occurs primarily through microplowing and microcutting mechanisms. In pure zinc, adhesive transfer from the counterface dominates, leading to large material loss through smearing and tearing. In contrast, the Zn-Al alloys show evidence of uniform shallow grooving consistent with abrasive wear, with periodic removal of thin layers through microcracking and delamination at the grain boundaries.

The depth profile of hardness through the overlay layer shows a characteristic gradient: the surface layer exhibits the highest hardness due to rapid solidification and fine grain structure, while the fusion zone shows reduced hardness owing to the dilution effect from the base metal. This gradient is beneficial for wear performance, as it provides a hard surface with a tougher substrate that resists fatigue cracking during cyclic loading.

Engineering Practice Implications and Recommendations

For practical application in pressure vessel fabrication and equipment repair, the following process recommendations emerge from the study:

1. Welding process selection: Submerged arc welding (SAW) is recommended for thick overlay layers (greater than 3 mm) due to its high deposition rate and low dilution. For thin layers (less than 1 mm), gas tungsten arc welding (GTAW) provides superior microstructural control.
2. Preheat temperature: A preheat of 150 to 250°C is necessary to prevent zinc vaporization and porosity formation. Temperatures above 300°C risk excessive grain coarsening in the base metal.
3. Shielding gas composition: When using GTAW or GMAW, a mixture of 90% argon and 10% CO₂ provides adequate protection while promoting favorable wetting of the zinc-based filler metal.
4. Post-weld heat treatment: Solution treatment at 280°C for 2 hours followed by water quenching improves the uniformity of the microstructure and reduces residual stresses without compromising hardness.

The dilution ratio between the base metal and overlay layer must be carefully controlled to maintain the desired alloy composition in the functional surface. For carbon steel substrates, a minimum overlay thickness of 2 mm is recommended to ensure the top 1 mm retains the target zinc-aluminum composition without significant iron contamination.

Study Insights and Conclusions

This research provides valuable insights into the design of zinc-based wear-resistant overlay coatings, bridging the gap between traditional galvanizing technology and modern weld overlay engineering. The key takeaway for practicing engineers is that zinc-based alloys, when properly alloyed and processed, can offer a cost-effective alternative to more expensive nickel-based or cobalt-based overlay systems for moderate wear environments.

The wear mechanism analysis demonstrates that the combination of hard intermetallic phases with a ductile matrix is essential for achieving high wear resistance in zinc-based systems. Future work should focus on optimizing multi-layer overlay designs that combine zinc-based wear layers with stainless steel or nickel-based corrosion layers to create composite coatings suitable for combined erosion-corrosion environments. The economic advantage of zinc-based systems, which cost significantly less than nickel-based alloys, makes them particularly attractive for large-area applications such as tank linings and heat exchanger surfaces where the total material cost of the overlay is a critical consideration.