High-Corrosion-Resistant Alloy Coating Empowers: Technological Upgrades of Aluminum-Zinc Coated Steel Strands Expand Diversified Applications

Driven by the continuous advancement of infrastructure projects in harsh environments such as offshore wind power, coastal bridges, and UHV power grids, aluminum-zinc coated steel strands have become a core growth driver in the high-end wire market, thanks to the excellent anti-corrosion performance of their "zinc-aluminum-rare earth" alloy coating. The domestic market size of aluminum-zinc coated steel strands is expected to exceed 8.5 billion yuan in 2025, with a year-on-year growth of 9.7%. The refined upgrading of production processes and optimization of alloy formulas are continuously enhancing the product's adaptability in extreme environments, providing long-term and reliable material support for infrastructure in multiple fields.​

Core Features: Three Core Advantages Solidify Market Competitiveness​

The core value of aluminum-zinc coated steel strands stems from the synergistic empowerment of "anti-corrosion + strength + durability," endowing them with significant competitive advantages in complex environments. Firstly, superior corrosion resistance is the core highlight. The zinc-5% aluminum-mixed rare earth alloy coating achieves dual protection through "sacrificial anode protection + barrier protection," with corrosion resistance 3-5 times higher than that of traditional hot-dip galvanized steel strands. It achieves over 1800 hours of no red rust in neutral salt spray tests, and a service life of more than 30 years in coastal high-salt-fog environments—2-3 times that of traditional products. Secondly, balanced mechanical properties: mainstream products have a tensile strength ranging from 1570MPa to 1960MPa, with some special models reaching 2160MPa, while maintaining an elongation rate of ≥4.5%. They can withstand long-term dynamic loads and complex stresses, meeting high-strength requirements such as main cables for long-span bridges and anchoring of wind power towers. Thirdly, wide scenario adaptability: product specifications cover φ12.7mm-φ28.6mm, with structures including 1×7 and 1×19. The coating thickness (120g/m²-610g/m²) can be customized according to needs, adapting to various harsh scenarios such as coastal infrastructure, desert wind power, and chemical parks. It also features sandstorm resistance, low-temperature tolerance (-40℃), and UV aging resistance.​

Production Process: Full-Process Precision Control Creates High-Quality Coatings​

The production of aluminum-zinc coated steel strands is a systematic project of "raw material purification - forming processing - alloy coating - finished product inspection." The core process focuses on coating uniformity and adhesion, with key procedures divided into five major links:​

Step 1: Raw Material Preparation and Surface Pretreatment​

High-quality high-carbon steel wire rods (carbon content 0.65%-0.85%) are selected as the base material, undergoing a four-step surface treatment of "pickling - alkaline washing - water washing - drying": pickling to remove oxide scale (hydrochloric acid concentration 18%-22%, temperature 40-50℃), alkaline washing (sodium hydroxide concentration 5%-8%) to remove oil, multi-stage water washing to neutralize residual acid and alkali, and finally hot air drying (temperature 120-150℃) to ensure a clean and dry steel base surface, laying the foundation for coating adhesion.​

Step 2: Wire Drawing Strengthening and Precision Control​

The pretreated wire rods are fed into a continuous wire drawing machine, adopting the "multi-pass progressive diameter reduction + online heat treatment" process to draw the steel wire to the preset diameter (e.g., φ5.0mm for 1×7 structure φ15.2mm steel strands). Meanwhile, sorbitic transformation is achieved through temperature control (450-550℃) to improve the tensile strength and toughness of the steel wire. A special graphite lubricant is used during wire drawing, with drawing speed (8-12m/s) and die precision controlled to avoid surface scratches, ensuring a surface roughness of Ra≤0.8μm.​

Step 3: Stranding Forming to Ensure Structural Density​

Multiple drawn steel wires (e.g., 6 side wires + 1 central wire for 1×7 structure) are fed into a stranding machine, stranded according to the preset lay length (12-16 times the diameter of the steel strand) and lay direction (left lay or right lay) to form the steel strand blank. High-end products additionally adopt a "pre-deformation process": mechanical pressure is applied to pre-bend the steel wires into an arc, resulting in a tighter structure after stranding, uniform stress distribution under load, and reduced risk of coating cracking caused by residual stress.​

Step 4: Alloyed Hot-Dip Plating (Core Process)​

This is the key link determining product performance, adopting the "hot-dip plating + alloying treatment" process: first, the steel strand blank is preheated to 450-500℃ to remove residual moisture and oil; then immersed in a zinc-5% aluminum-mixed rare earth alloy molten bath (aluminum content 4.2%-5.8%, total rare earth elements Ce/La 0.05%-0.15%) at 455-465℃ for 3-5 seconds to ensure uniform coating adhesion; after being lifted out, the coating thickness is controlled by air knife blowing (pressure 0.3-0.5MPa), followed by heat preservation in an alloying furnace (temperature 500-550℃) for 10-15 seconds to trigger a metallurgical reaction between the zinc layer and the steel base, forming a Zn-Fe-Al ternary alloy layer that enhances coating adhesion (peel strength ≥15N/mm) and corrosion resistance.​

Step 5: Post-Treatment and Finished Product Inspection​

The aluminum-zinc coated steel strands are rapidly cooled by water (temperature ≤60℃), then subjected to passivation treatment (chromium-free passivation solution, thickness 0.5-1.0μm) to enhance anti-discoloration and corrosion resistance. Finished product inspection adopts a "online + offline" dual mode: online control of outer diameter tolerance (±0.02mm) via laser diameter gauge and eddy current testing for coating continuity and thickness uniformity; offline sampling for tensile strength, coating adhesion, salt spray test, bending test, etc., to ensure compliance with GB/T 20492-2019 national standard, with unqualified products directly rejected.​

Technological Upgrades: Dual Breakthroughs in Alloy Optimization and Intelligent Production​

The aluminum-zinc coated steel strand industry is accelerating its transformation towards "high performance + low carbonization." In terms of technological innovation, enterprises continuously optimize alloy formulas: adding trace rare earth elements (Ce, La) to refine coating grains and reduce porosity, improving corrosion resistance by an additional 15%-20%; some leading enterprises have developed Zn-Al-Mg ternary alloy coatings, with corrosion resistance 20%-30% higher than traditional formulas, currently in the pilot-scale test phase. In intelligent production, leading enterprises have introduced AI closed-loop control systems to real-time adjust parameters such as molten bath temperature, air knife pressure, and stranding speed, controlling coating thickness tolerance within ±5μm and increasing the first-pass qualification rate to 99.7%; machine vision inspection technology enables millisecond-level identification of surface defects (e.g., coating exposure, scratches), with inspection efficiency 10 times higher than manual inspection. In green production, the penetration rate of cyanide-free passivation technology has reached 90%, replacing traditional chromium-containing processes; the utilization rate of recycled zinc has increased to 85%, unit product energy consumption has decreased by 18.7% compared with 2020, and carbon emission intensity has dropped below 0.8tCO₂/t, meeting the compliance requirements of the EU Carbon Border Adjustment Mechanism (CBAM).​

Market Application: Extreme Scenario Demand Drives Multi-Field Growth​

The application scenarios of aluminum-zinc coated steel strands continue to expand into harsh environments, forming three core growth poles: "coastal infrastructure + new energy + transportation engineering." In coastal infrastructure, the proportion of aluminum-zinc coated steel strands in coastal bridge projects in Guangxi and Fujian has exceeded 40%, used for main cable suspension and pile foundation anchoring to solve anti-corrosion problems in marine environments. In new energy, offshore wind power projects have driven a surge in demand, with an expected growth rate of 28% in 2025, used for wind power tower anchoring and submarine cable protection. In transportation engineering, high-corrosion-resistant aluminum-zinc coated steel strands are adopted in projects such as the Sichuan-Tibet Railway and cross-sea bridges, adapting to complex environments such as high cold, high altitude, and strong UV radiation. Additionally, demand from overseas projects along the "Belt and Road" is robust: export volume is expected to reach 32,000 tons in 2025, a year-on-year increase of 12%, mainly supplying power grid upgrading and infrastructure projects in Southeast Asia, the Middle East, and other regions.​

Industry experts stated that aluminum-zinc coated steel strands will develop towards "higher corrosion resistance, lower energy consumption, and intelligent perception" in the future. The industrialization of Zn-Al-Mg alloy coatings and intelligent monitoring products integrated with optical fiber sensing will become key R&D focuses. Enterprises need to continuously focus on alloy formula optimization, precise process control, and green production transformation to seize the competitive high ground in the wave of extreme environment infrastructure, providing long-term anti-corrosion material solutions for global infrastructure.