Study On The Alloying Of7072Al Alloy For Cladding Layer Of Heat-exchanger

7072Al alloy is one of the most important thermal transport materials,which has been commomly used as the aluminium clad alloys in heatexchanger. In this thesis, the effect of rare earth element Ce and transitionelement Ti addition on the microstructure, mechanical properties andelectrochemical properties of simulated-brazing7072Al alloy wereinvestigated through TEM, SEM, tensile tests and Tafel polarization analysis.The influence of heat-treatment on the mechanical properties7072Al alloywas also studied.Transmission electron microscopy (TEM) observations revealed that,the addition of Ce could have an effect on the microstructure ofsimulated-brazing7072Al alloy,0.15%Ce addition made grains finer, theprecipitates denser and its shape spherized; when the content increased to0.25%, grains turned to be more irregular, the Ce increase also coarsened theprecipitates and the precipitates became less dense, which worsened themechanical properties of7072Al alloys at RT; Ce-containing alloy showedhigher strength than7072Al alloy in elevated temperatures, and the more the Ce content was, the higher the strength was. Annealling had unfavorableeffect on the mechanical properties of the simulated-brazing alloy, however,this adverse effect could be weakened due to the addition of Ce element. Theelectrochemical testing results indicated that0.15%Ce addition to the alloysalso had great impact on the corrosion potential of the simulated-brazingalloys in0.5%NaCl solution, which made the corrosion potential shifted topositive direction by35mV, but the over dose of Ce could weaken the goodeffect; In1M NaCl+0.3M H2O2solution, Ce barely had any influence on thecorrosion potential.TEM observations revealed that, when the alloys were insimulated-brazing state, there was no much difference in the microstructurein Ti-free alloy and Ti-containing alloy, only the former has densierprecipitstes; Ti addition could reduce the precipitates, which led to thedecrease of mechanical properties at RT. But Ti addition could enhance thestrength in temperatures above150°C, further more, σbcould increased by10mV at200°C. Annealing has adverse effect on comprehensive mechanicalproperties of the simulated-brazing Ti-containing alloy and Ti-free alloy, butthe effect on the former is weaker. Ti addition to7072Al alloy could alsoimprove its corrosion resistance by shifting the corrosion potential to thepositive direction, but not the same way as Ce did. For Ti addition, the improvement in0.5%NaCl solution was slightly weaker but in1MNaCl+0.3M H2O2solution, much stronger.