Coating Types for Pre-painted Steel: GI, GL, ZAM? What are the differences

When selecting pre-painted steel sheets (PPGI, PPGL), the substrate material is always mentioned. The substrate is one of the core factors determining the product’s anti-corrosion lifespan, application scenarios, and cost-effectiveness. Currently, the popular coated steel sheets on the market include Galvanized (GI), Galvalume (GL), and Zinc-aluminum-magnesium (ZAM). Today, let’s understand these three mainstream coatings from multiple perspectives such as composition, appearance characteristics, performance differences, and application scenarios.

Galvanized VS Galvalume VS Zinc-aluminum-magnesium

Comparison Dimension	Galvanized (GI)	Galvalume (GL)	Zinc-aluminum-magnesium (ZAM)
Composition	Pure Zinc	55% Al, 43.4% Zn, 1.6% Si	Zn + Al + Mg
Appearance	Visible spangle / zero spangle, silvery white	No spangle, silver-gray matte	Extremely smooth, silver-gray with a slight bluish tint
Corrosion Resistance	Baseline	2-6 times	5-10 times
Cut-edge Protection	General	Excellent	Excellent (Self-healing)
Heat Resistance	≤230°C	≤315°C	200-300°C
Heat Reflectivity	General	Excellent (80%)	Good
Formability	Excellent	Good	Excellent
Cost	Low	Medium	Medium-High
Main Applications	General construction, interior of home appliances	Building envelopes, high-temperature components, coastal areas	Automotive, precision manufacturing, harsh environments

Coating Composition Comparison

Coating Type	Composition Ratio	Code Example
Galvanized	Zn (Pure Zinc) ≈ >99%	GI, Z
Galvalume	55% Al, 43.4% Zn, 1.6% Si	GL, AZ
Zinc-aluminum-magnesium	Mainly Zn, with small amounts of Al, Mg (typically Al 1-11%, Mg 0.1-3%)	ZAM, ZM, SuperDyma

Appearance Characteristic Comparison

Aspect	Galvanized Steel	Galvalume Steel	Zinc-aluminum-magnesium Steel
Appearance	HDG: Snowflake-like or shiny crystals; EG: Zero spangle or fine spangle	Uniform fine spangle	Extremely smooth and uniform
Color	Silvery white	Silver-gray matte	Slight silver or blue-gray tone
Texture	Relatively smooth, but with crystalline texture	Fine and smooth	Extremely flat, very high surface quality

Performance Comparison

Corrosion Resistance

Coating Type	Corrosion Resistance	Cut/Scratch Protection	Chemical Resistance
Galvanized	Medium	Zinc sacrifices to protect substrate	General, not resistant to acids/alkalis
Galvalume	2-6 times of GI	Al barrier + Zn sacrifice, more durable protection	Excellent, resistant to industrial atmosphere, high temp
Zinc-aluminum-magnesium	5-10 times of GI	Exceptional; Mg promotes dense protective film, strong cut-edge self-healing	Superior, resistant to salt spray, ammonia, acids/alkalis

Heat Resistance & Heat Reflectivity

Coating Type	Long-term Heat Resistance	Heat Reflectivity	Applicable Scenarios
Galvanized	≤230°C	General	Ambient temperature environments
Galvalume	≤315°C	Excellent (~80%)	High-temp roofs, chimneys, oven components
Zinc-aluminum-magnesium	200-300°C	Good	General high-temp environments

Formability

Coating Type	Bending/Stamping Performance	Coating Adhesion	Weldability
Galvanized	Excellent, mature process	Good	Requires attention to zinc fumes, weldable
Galvalume	Good, needs attention to T-bend parameters	Excellent, suitable for deep processing	Slightly difficult welding, parameters need adjustment
Zinc-aluminum-magnesium	Excellent, adapts to extreme forming	Excellent, strong coating-substrate bond	Better weldability than GL, less fumes

Self-healing / Cut-edge Protection

Coating Type	Cut-edge Protection Mechanism	Effect
Galvanized	Sacrificial protection of zinc, but consumes quickly	Effective short-term, possible red rust spread
Galvalume	Aluminum forms dense oxide film at cut, blocking corrosion	Long-lasting effect, very slow red rust spread
Zinc-aluminum-magnesium	Mg promotes dense, conductive protective film for efficient electrochemical protection	Best effect, strong cut-edge self-healing, red rust hardly spreads

Application Scenarios

Application Field	Recommended Coating	Reason
General Industrial Plants/Warehouses	Galvanized (GI)	Low cost, meets basic anti-corrosion needs
Civil Building Roofs/Walls	Galvalume (GL)	Balances corrosion resistance and heat resistance
Coastal/High Salt Spray Areas	ZAM or High-coating GL	Extreme salt spray resistance + excellent cut-edge protection
High-temperature Environments (Chimneys, Ovens)	Galvalume (GL)	Best heat resistance + high heat reflectivity
Automotive Precision Stampings	ZAM	Excellent formability + cut-edge protection
Agricultural/Livestock Buildings	ZAM	Resistant to ammonia corrosion + cut-edge self-healing
Home Appliance Back Panels/Internal Parts	Galvanized (GI)	Cost priority + good formability
High-end Appliance Face Panels	Galvalume/ZAM + Color coating	Fine surface + good coating adhesion
Photovoltaic Brackets	Galvalume or ZAM	25-year lifespan requirement + strong weather resistance

Wanzhi Group: Matching You with the Most Suitable Coating Solution

As a professional metal material supplier, Wanzhi Group can provide a full range of coated products, as well as spraying or coil coating processing services.

Metal Coatings

• Galvanized (GI) Series: Z30-Z275, regular spangle/zero spangle, meeting general needs, maximum coating weight up to 600g/㎡.
• Galvalume (GL) Series: AZ30-AZ150, the preferred choice for building envelopes, maximum coating weight up to 200g/㎡.
• Zinc-aluminum-magnesium (ZAM) Series: ZM30-ZM150, designed for harsh environments and precision manufacturing.

Color Coatings

• PPGI: Based on Galvanized Steel (GI) substrate, paired with Polyester (PE), Silicon Modified Polyester (SMP), High Durability Polyester (HDP), Polyvinylidene Fluoride (PVDF). Economical and versatile, suitable for most常规 environments.
• PPGL: Based on Galvalume Steel (GL/55% Al-Zn) substrate, also paired with PE, SMP, HDP, PVDF. Suitable for scenarios with high requirements for anti-corrosion and heat resistance.

We not only supply substrates and pre-painted steel but also provide one-stop services including slitting, leveling, profiling, punching, and bending. Our products comply with international standards such as EN, ASTM, JIS, GB, and third-party inspection reports are available. Unsure which coating to choose for your project? Contact us today to get solutions and sample testing support based on your specific application scenario!