Galvalume Steel Coil Sheet

The galvalume & aluzinc steel sheet in coil uses the cold-rolled steel sheet as a substrate and solidified by 55% aluminum, 43.4% zinc and 1.6% silicon at 600 °C. It combines the physical protection and high durability of aluminum and the electrochemical protection of zinc. It is also called aluzinc steel coil.

Advantage:

  • Strong corrosion resistance, 3 times that of galvanized steel coil.
  • The density of 55% aluminum is smaller than the density of zinc. When the weight is the same and the thickness of the plating layer is the same, the area of the galvalume steel sheet is 3% or larger than that of the galvanized steel sheet.

Surface Finish of Galvalume Steel

Normal(non-skinpassed)spangleSkinpassed spangleRegular spangleMinimized spangle

Weight of AI-Zn coating

The recommended nominal Al-Zn alloy coating weight is listed in the table below. Considering the use environment of galvalume steel sheet for construction purposes, the recommended minimum nominal coating weight is 50/50 g/m².

Coating typeRecommended coating weight
Al-Zn alloy30/30,40/40,50/50,60/60, 75/75,90/90
a: Coating mass 50g/m: equals to a coating thickness of 13.3pm approximately.

Surface Treatment of Galvalume Steel Sheet

ItemClassificationSymbol
Coating typeAl-Zn alloyAZ
Surface finishRegular spangleR
Minimized spangleM
Skin passedS
Surface treatment Chromate passivatedc
Non-chromate passivatedC5
Chromate passivated + oilingCO
Non-chromate passivated+oilingCO5
Anti-fingerprintN
Non-chromate anti-fingerprintN5
Non-chromate high weather resistance anti-fingerprintNW
Oiling0
No treatmentU

Galvalume Steel Coil Coating Layer

  • Anti-Finger printing ,Chromated, Oiled/ non-oiled
  • Alu-Zinc Plating Layer
  • Cold Rolled Steel Sheet

Aluzinc Steel Sheet Process

Decoiling – Cleaning – Annealing – Zinc pot – Cooling – Air knife – Straightening – Post-treatment – Coiling

Detailed steps of the galvalume steel sheet processing

Step 1:

Pre-treatment: After the cold-rolled coil arrives in the galvalume workshop, after passing through the uncoiler, through the degreasing section and the reduction furnace, the steel coil is cleaned and its components are reduced to the extent that it can be galvanized.

Step 2:

Central section: The most critical technology is this step. After passing through the zinc pot, a layer of zinc layer is plated on the surface of the steel plate. After coming out of the zinc pot, it is cooled and shaped by the cooling tower.

Step 3:

Post-processing: The steel plate finally comes to the post-processing stage after various processes. After finishing, straightening and passivation, and finally coiling.

Galvalume Steel Coil Features

  • Thermal Reflection:

People use it as material for heat-insulation for its thermal reflectivity as high as twice the galvanized steel sheet.

  • Heat-resistance:

The aluzinc steel sheet could bear above 300℃ high temperature with its good performance in heat-resistance, quite similar to the aluminized steel sheet’s performance in oxidation-resistance under high temperature. It is often used for chimney pipe, oven, illominator, and fluorescent lamp cover.

  • Corrosive-resistance performance:

The essential of galvalume steel coil’s corrosive-resistance lies at aluminium’s protective property. Once the zinc come under abrasion, the aluminium would form a layer of densified oxidized aluminium, preventing the interior from further corrosion.

  • Economical:

The density of 55%AL-Zn is smaller than Zn, therefore, with the same weight and thickness of coating, the galvalume steel sheet is 3% larger in area than that of galvanized steel sheet.

  • Easily painted:

There is perfect adhesiveness between galvalume sheet and paint, saving the process of pre-treatment and weathering for painting work.

The coating material on the galvalume steel sheet is outstanding in its adhesiveness, which could be directly tarring on the advertising board and commonly used board with no pre-treatment such as weathering process.

  • The galvalume steel sheet’s surface is luxury in silver colored appearance.
  • Galvalume steel sheet and galvanized steel sheet are similar in performance of processability and painting.

Applications for Galvalume Steel Sheet

Construction: civil and industrial building roofs, facades, substrates for painted rolls, garage doors.

Industrial instruments: electric control cabinets, industrial freezers, vending machines.

Usually, building roofs are the most widely used.

 
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Galvalume Steel Coil FAQ

galvalume coil vs galvanized coil

The primary difference lies in its coating layer. For the galvanized sheet, a layer of zinc material is averagely distributed on the surface of galvanized sheet, playing as a positive sheet protective to the base metal, in another word, zinc works as a substitute for corrosive-proof protecting the base metal until it is torn off.

While the galvalume sheet’s surface is a coating layer consisting of 55% aluminium, 43.5% zinc and other few elements, which appears a honeycomb structure under microscopic observation. Aluminium honeycomb wraps the zinc. Under such circustances, even though the coating of galvalume also plays its protective role as a positive sheet, however, such protection decrease sharply due to declining content of zinc and no easy electrolysis when zinc wrapped by aluminium.

Therefore, once the galvalume sheet is cut open, the verge of cut would be generally losing its protector and quickly go rusting. So we should cut as less as possible, once cutting happen, use anti-rusting paint or zinc-rich paint for protecting the verge, extending its lifespan.