The Effect Of Alloy Elements Addition On Hot-dipped Zn-10~15%Al Alloy Coatings

As Zn-Al alloy has the advantage of the sacrifice protection of galvanizecoating and the isolation protection of hot dip aluminize coating, Zn-Al alloybecome a research hotspot in recent years. In general, it needs add a small quantityof silicon into Zn-55%Al alloy, as called Galvalume, and add a small quantity ofmagnesium and RE into Zn-0.5⁶%Al alloy. However, there was less involved in theopening literature of the effect on Zn-10¹5%Al coating microstructure andperformance by adding alloy elements silicon and magnesium. The effect of siliconand magnesium on the microstructure and performance of hot dipped Zn-10¹5%Alcoating was studied in this essay by scanning electron microscopy （SEM）, energydispersive spectrometer （EDS）, X-ray diffraction（XRD） and other instruments andequipments.The effect of silicon and magnesium on the microstructure and performance ofhot dipped Zn-10¹5%Al coating was studied in this essay. The experimental resultsshow that aluminum can inhibit the Fe-Zn reaction, and form the alloy layer whatconsisted of Fe₂Al₅and FeAl₃. And also, silicon can strongly inhibit the Fe-Alreaction and reduce the thickness of the coating. To get straight and continuous alloylayer, the addition of silicon should be0.2%in the Zn-10%Al coating and0.4%inthe Zn-15%Al coating. when the addition of silicon comes to0.4%in the Zn-10%Al coating or0.6%in Zn-15%Al coating, the phase constituent of the alloy layerchange from Fe₂Al₅and FeAl₃to ternary phase τ4. Most of silicon gather at thejunction of alloy layer and substrate while inhibit the Fe-Al reaction, the rest of thatform elemental silicon in the free layer of coating. Studies on the kinetics growth ofalloy layer show that the growth of alloy layer is mainly controlled by diffusion afteradding silicon, and become a decrease in growth rate of alloy layer. As come tomagnesium, the experiments found that magnesium can promote the growth of alloylayer, accelerate the rate of FeAl₃peeling from Fe₂Al₅layer. And also, magnesiumcan fine grain size of free layer. But the phase constituent of the alloy layer still beFe₂Al₅and FeAl₃with increasing magnesium content in the bath.The experimental results show that the surface quality of coating is good whenadding1.0%Si or1.5%Mg in the Zn-15%Al coating. The results of neutral salt-spray test show that the Zn-15%Al-1.0%Si coating and the Zn-15%Al-1.5%Mgcoating has excellent corrosion resistance. Based on XRD results, silicon has littereffect on corrosion products produced by neutral salt-spray test. The corrosionproducts of Zn-Al-Si coating are Zn（OH）₂and Zn₅（OH）₈Cl₂H₂O, but the corrosionproducts change to Zn₅（OH）₈Cl₂H₂O only as addition of magnesium in Zn-15%Albath. Magnesium accelerate the corrosion products change from Zn（OH）₂andZn₅（OH）₈Cl₂H₂O to Zn₅（OH）₈Cl₂H₂O only, and promote the corrosion productlayer of coarse grain and loose structure change into a layer with refinedmicrostructure and tightly bound to the coating surface, thus improve the corrosionresistance of coating.