Surface protection — galvanising is best described as which of the following surface treatment processes for steel?

Introduction / Context:
Protective coatings extend the life of steel structures and hardware by preventing corrosion. Galvanising is one of the most economical and widely used methods to provide sacrificial protection via zinc. The question probes recognition of the correct definition among related processes.

Given Data / Assumptions:

• Consider conventional hot-dip galvanising on structural steel.
• Distinguish from diffusion-based or conversion coatings.
• Focus on the core process definition.

Concept / Approach:

In hot-dip galvanising, cleaned steel is immersed in molten zinc, forming metallurgically bonded zinc-iron alloy layers topped with zinc. The coating provides barrier protection and sacrificial (cathodic) protection at damaged spots. Zinc diffusion into steel at lower temperatures is a different process called sherardising. Phosphate coatings are thin conversion layers used primarily as paint bases and for wear reduction, not as thick sacrificial coatings.

Step-by-Step Solution:

Verification / Alternative check:

Standards such as ISO 1461 and ASTM A123 define galvanising as hot-dip zinc coating of iron and steel products.

Why Other Options Are Wrong:

“Zinc diffusion process” describes sherardising; “thin phosphate coating” describes phosphating; “none of the above” is incorrect because hot-dip is correct.

Common Pitfalls:

Confusing various zinc-related treatments; assuming all zinc processes are the same in mechanism and coating thickness.

Final Answer:

process of coating zinc by hot dipping