Wetting Behavior And Interfacial Structures Of Molten Al 6061 And 4043 Alloys On The Surfaces Of Different Metals

Due to the excellent inoxidizability of Aluminum alloys,it receives significant attention for hot-dip aluminizing process.The coating obtained by the hot dip aluminum technology using steel and titanium as matrix metal,not only can improve anti-corrosion of the whole structures at room temperature but also can improve inoxidizability under high temperature.The hot dip aluminized copper surface can avoid more brittle phase in the process of Al-Cu joining.Such a process achieves effective joining of Al-Cu composites.The realization of hot dip aluminum process and coating quality control was closely related to wettability.Meanwhile,good wettability of matrix metal by solder is one of the important factors to obtain excellent welded joint.In this work,T2 Cu,Q235steel,TA2 pure Ti and TC4 Ti alloy were selected as matrix metals.The wetting behavior and interfacial structures of different metal surface by two commercial grades Al alloys(Al 4043 and 6061 alloy)were investigated.It is expected that such a study could provide a substantial guidance for the hot dip aluminizing processes.Firstly,Wetting of T2 Cu by two industrial grade Al alloys(i.e.,Al 6061 and 4043 alloys)were studied by sessile drop method at 650~750oC under high vacuum.The results showed that Al/Cu system was a typical dissolution wetting at 650~700 oC,wettabilities are dependent on temperatures and can be improved with the increase of temperature;At 700~750 oC,wettability have no direct relationship with temperature,the final equilibrium contact angle was ~ 21o;The interfacial stratification based on the dissolution-precipitation theory can be divided into three layers;The amount of molten aluminum alloy is decreasing at triple line zone,and the dissolution Cu is more easy to reach saturation and then precipitate intermetallics.The formed intermetallic layer would block mass transfer at the close of triple line zone of the solid-liquid interface,and then block the spreading;spreading dynamics can be described by dissolution process controlled model.The spreading of Al 6061 and 4043 alloy drops is nonlinear.The wetting activation energies were 52 kJ/mol and 57 kJ/mol,respectively.Secondly,Wetting of metal substrates(i.e.,Q235 steel,TC4 Ti alloys and TA2 pure Ti)by two industrial grade Al alloys(i.e.,Al 6061 and 4043 alloys)were studied by sessile drop method at 600~750 oC under high vacuum.The results showed that Al/steel and Al/Ti systems were the typical reactive wetting;wettabilities are dependent on the temperatures and can be improved with the increase of temperature.The small amount of alloying element Si and Mg in the Al alloys can cause differences in the interfacial structures and final wettability.The segregation of Si at liquid/solid interface satisfies the thermodynamic conditions.The formation of the Si-rich phase(Fe2(Al1-xSix)5 and Ti7Al5Si12)at solid-liquid interface,as a compact intermetallic layer would block the mass transfer at solid-liquid interface and deteriorate wettability.Si-rich phase(Ti7Al5Si12)was unstable,would decompose with the increasing temperature and then transfer to Al3 Ti at triple line zone.The main role of intermetallic compounds(Fe2Al5 and Al3Ti)in the wetting of metal/metal system was removing the oxide film,and promoting interfacial reaction of aluminum alloy with the substrate;Mg vapor(that around the drop)would reduce the oxide film when the metallic substrate was covered with the very thin oxide film,make substrate surface to appear metallic characteristic.When the drop contact and react with such a pure substrate,the formed loose phase(Fe2Al5 and Al3Ti)at triple line zone would remov the oxide film and promote wettability.The spreading dynamics can be described by reaction product control model.For 6061Al/Q235 steel system,the wetting behaviors have the characteristic of linear spreading.For 6061Al/Ti system,the wetting behaviors can be divided into two stages,i.e.,first nonlinear spreading and then linear spreading;For Al 4043 alloy system,the wetting behaviors have the characteristic of nonlinear spreading;All spreading activation energies are related to the intensity of interfacial reaction.Finally,a significant precursor film was observed in the above reaction wetting systems.The formation of precursor film depends on the temperatures.The formation of precursor film always accompanies with the good final wettability,and the width of precursor film increased with increasing temperature.The formation mechanism of precursor film is “subcutaneous infiltration”.