1. The Hot Dip Galvanizing Process
Hot dip galvanizing coats the steel angle with a layer of zinc that protects the base metal in two ways. The steel is first degreased and pickled to remove oil and scale, then dipped into a bath of molten zinc at about 450°C. A series of zinc iron alloy layers forms on the surface and bonds metallurgically to the steel, topped by a pure zinc layer. The coating thickness is controlled by the immersion time and the bath chemistry and is verified against the project standard.
2. Common Sizes and Material Grades
Galvanized angles in the 38mm, 40mm and 50mm range are the most frequently used sizes for outdoor frames and supports. Typical sections are 38x38x4, 40x40x4 and 50x50x5, and the base material is supplied in Q215, Q235 and Q355 grades. Q235 gives a minimum yield strength of 235 MPa and is the standard choice for general framing, while Q355 is selected where higher loads require a stronger section without increasing the size.
| Section | Grade | Typical Use |
| 38x38x4 | Q215 / Q235 | Light frames and brackets |
| 40x40x4 | Q235 | General outdoor framing |
| 50x50x5 | Q235 / Q355 | Fences, racks and supports |
3. Corrosion Protection and Coating Quality
The zinc coating protects the steel by acting as a barrier and by corroding preferentially at damaged areas, so scratches and cut edges are still protected by the surrounding zinc. The coating thickness for angles is normally specified to ASTM A123 or GB/T 13912, with a typical local thickness of 55 to 85 micrometers for these sizes. Where the angle is cut or drilled after galvanizing, the exposed steel should be repaired with a zinc rich paint to restore the protection.
4. Fabrication and Handling
Galvanized angles can be cut and drilled, but the operations should be planned so that most holes are made before galvanizing. When drilling after coating, the hole should be touched up with zinc rich paint. The angle can be welded after galvanizing, but the zinc fumes must be controlled and the weld area cleaned and coated afterwards. The sections are stored on racks with airflow between them to avoid white rust from trapped moisture.
5. Typical Outdoor Applications
Frames for fences, gates and security barriers.
Supports for solar panels and communication equipment.
Frames for signs, canopies and shelters.
Transmission line and substation structures.
Agricultural buildings, greenhouses and livestock equipment.
Frequently Asked Questions
Q: How long does a galvanized angle last outdoors? In a normal urban or rural atmosphere a coating of 55 to 85 micrometers typically protects the steel for 30 to 50 years before maintenance is needed, depending on the environment.
Q: What is the difference between electro galvanizing and hot dip galvanizing? Hot dip galvanizing gives a much thicker coating with metallurgical bonding, while electro galvanizing is thin and is used for indoor parts; hot dip is the standard for outdoor structural angles.
Q: Can the angle be painted after galvanizing? Yes, the zinc surface can be painted with a suitable primer and top coat, and the combination is called a duplex system, which gives the longest service life.
Q: Are Q215 and Q235 the same steel? They are from the same carbon steel family; Q215 has a minimum yield strength of 215 MPa and Q235 of 235 MPa, so Q235 is preferred for structural frames and Q215 for light duty parts.
Q: How is the coating thickness measured? The thickness is measured with a magnetic thickness gauge on the flat surfaces of the section, and the average and minimum values are checked against the coating specification.