Views: 109 Author: Sara Zhang Publish Time: 2026-05-15 Origin: Tsingri Screw
Solar energy projects are among the most demanding environments for construction fasteners. Unlike a standard industrial building that might have a design life of 15 to 20 years before major maintenance, utility-scale solar arrays are engineered for a minimum 25-year operational lifespan.
During those 25 years, the fasteners are exposed to constant thermal cycling, UV radiation, and — most critically — the complex electrochemical environment created by joining dissimilar metals in outdoor conditions.
This article explores why bi-metal self-drilling screws are not just a premium choice, but a technical necessity for modern solar mounting systems, focusing on the prevention of galvanic corrosion and the mechanical demands of large-scale arrays.
Most modern solar racking and mounting systems rely on two primary materials:
Aluminium Rails and Clamps: Aluminium (typically 6005-T5 or 6063-T5) is the preferred material for mounting rails due to its high strength-to-weight ratio and its natural ability to resist atmospheric corrosion through the formation of an oxide layer.
Steel Substructures: These aluminium rails are then fixed to a steel substructure — often galvanised steel purlins, C-channels, or cold-formed steel framing.
This interface creates a classic engineering dilemma. You need a fastener that can drill through structural steel (requiring high hardness) but will not cause the aluminium rail to fail through corrosion (requiring electrochemical compatibility).
When two dissimilar metals (like aluminium and carbon steel) are in electrical contact in the presence of an electrolyte (rainwater, dew, or humidity), a galvanic cell is formed. One metal becomes the anode and the other the cathode.
In the aluminium-steel pairing:
Aluminium is the more active (anodic) metal.
Carbon Steel is the more noble (cathodic) metal.
The result is that the aluminium rail sacrificially corrodes to protect the steel fastener. This corrosion manifests as white powdery deposits (aluminium oxide) around the fastener head, followed by pitting and eventually "ovalling" of the hole. When the hole becomes larger than the fastener head or the washer's seal, the mechanical integrity of the mounting system is compromised. The array can shift under wind loads, potentially leading to catastrophic failure during a storm.
A bi-metal self-drilling screw is a hybrid fastener designed specifically to bridge the gap between mechanical drilling performance and electrochemical safety.
The shank and head of a TGR bi-metal screw are manufactured from austenitic stainless steel (SS304 or SS316). Stainless steel sits much closer to aluminium on the galvanic series than carbon steel does. By using a stainless body, the "potential difference" that drives galvanic corrosion is significantly reduced. The aluminium rail remains structurally sound for the full 25-year life of the project.
Austenitic stainless steel is too soft to drill through structural steel. To solve this, TGR bi-metal screws feature a high-tensile SCM435 alloy steel drill point welded to the stainless body. This point is heat-treated to Rockwell C 50-55, allowing it to drill through 2.0mm to 3.0mm steel purlins with the same speed and ease as a standard carbon steel screw.
When specifying bi-metal fasteners for utility-scale solar, three features are non-negotiable:
For fixing aluminium rails to steel, TGR recommends the Double Thread design. The first thread start engages the aluminium rail, while the second start engages the steel purlin. This creates a dual-locking mechanism that resists vibration loosening caused by constant wind-induced "fluttering" of the solar panels.
In solar installations, the fastener is often hidden under the panel or rail, where moisture can be trapped. A standard loose rubber washer can perish or slip during installation. A bonded washer (where the EPDM is chemically fused to a stainless steel backing) ensures a permanent, watertight seal that won't degrade under decades of UV exposure.
While the body of the screw is stainless, the SCM435 drill point is still a carbon-alloy steel. At TGR, we apply a high-performance Ruspert or REXIUBAO coating to the drill point. This ensures that the tip does not become a site for rust initiation during the installation phase or in the event of minor condensation within the purlin.
Bi-metal screws carry a higher initial cost than coated carbon steel fasteners. However, in utility-scale solar, the "cost of failure" is astronomical.
If a project uses carbon steel fasteners that lead to galvanic corrosion:
Remediation: Replacing thousands of fasteners on a live solar farm is a logistical nightmare.
System Downtime: Maintenance windows require segments of the array to be decommissioned.
Warranty Risk: Most solar panel and racking manufacturers will void their warranties if non-compatible fasteners are used.
Specifying bi-metal fasteners from the outset is a form of project insurance. It ensures that the smallest component in the system (the screw) does not become the reason the largest investment (the array) fails.
As solar projects move into increasingly aggressive environments — from coastal salt-spray zones to high-humidity tropical regions — the margin for error in fastener selection is disappearing.
For any installation involving aluminium rails fixed to steel substructures, bi-metal self-drilling screws are the only technically sound choice. They combine the drilling power of high-tensile steel with the life-long corrosion resistance of stainless steel, ensuring that your solar investment stays secure for the next quarter-century.
For technical data sheets, pull-out test reports, or custom solar fastening solutions, contact our engineering team at info@tsingri.com.
