Galvannealed (GA) Steel

Specification Parameters

Parameters of Galvannealed (GA) Steel
Parameter Category	Specific Parameter	Typical Value / Description	Importance / Effect
Coating Process	Process	Hot-dip galvanized steel sheet that is immediately heat-treated (annealed) in-line.	The annealing process diffuses iron from the steel substrate into the zinc coating, forming a zinc-iron alloy layer.
Coating Properties	Coating Mass/Weight	Mass: 30 to 100 g/m² (total both sides)	Specifies the amount of zinc-iron alloy coating, which provides both corrosion protection and a superior surface for painting.
	Coating Mass/Weight	Common Designation: A40 (40 g/m²), A60 (60 g/m²), A80 (80 g/m²)
	Coating Composition	Typically 90-95% Zinc, 5-10% Iron	The iron content is critical, giving the coating its matte grey appearance, weldability, and paint adhesion properties.
	Coating Structure	100% Zinc-Iron intermetallic alloy (delta phase)	The entire coating is a diffusion-bonded, brittle alloy layer with a matte grey, rough surface ideal for paint adhesion.
	Surface Morphology	Matte grey, uniformly rough, porous	The rough, porous surface provides excellent mechanical paint adhesion and a superior substrate for phosphating.
Performance	Corrosion Resistance	Excellent, but slightly less than pure galvanized (GI) of equivalent weight. The iron in the coating sacrifices itself.	Provides long-term corrosion protection, especially after painting (the combination is superior to either alone).
	Weldability	Excellent	The conductive, iron-rich coating is more compatible with resistance spot welding than pure zinc coatings, reducing electrode wear and spatter.
	Paint Adhesion	Superior. Excellent for both mechanical bonding (rough surface) and chemical bonding (phosphating).	The primary reason for choosing GA over GI. It prevents paint peeling or blistering, especially during forming.
	Formability	Fair to Good. The alloy coating is brittle and can develop fine powdering (smut) or micro-cracking when severely formed.	Not typically recommended for deep-drawing applications where GI's ductile coating is better. The micro-cracks are sealed by paint.
Testing	Bend Test	More prone to fine powdering on the outer bend radius compared to GI.	Used to check for excessive powdering, which could affect paint appearance.
Testing	Phosphate Weight	High (e.g., 2.0 - 3.5 g/m²)	Measures the effectiveness of the pretreatment process before painting. GA's surface allows for a heavy, uniform phosphate layer.