The Effect Of Zr, Cr On Hot-tearing Susceptibility And Mechanical Properties Of 3-series Deformed Aluminum Alloys

Aluminum heat exchangers have been widely used in the automotive industry,as a direction of low density,it can reduce car's weight,and reducing production costs at the same time.Three-layer aluminun brazing sheets are now widely used in heat exchangers,and one of the most important direction is to develop the high strength and high elongation core layer.In the actual production,we found that adding Zr and Cr to the three-series aluminum alloy used for producing the core layer can improve its mechanical properties,but increase the tendency of the alloy's hot-tearing during the casting state.The effect of different contents of Zr and Cr on hot-tearing susceptibility and mechanical properties based on the 3Z23 alloy were studied.In this paper,the effects different contents of Zr and Cr on hot-tearing susceptibility of 3Z23 alloy were studied.And the hot-tearing susceptibility of the alloy was evaluated by CRC die method.It was shown that Zr and Cr can significantly increase the hot-tearing tendency of the alloy.The analysis shown that the addition of Zr and Cr can increase the grain size of the casting alloys and affects the primary phase in the grain boundary.So in the end of solidification,the larger the grain size,the larger the intergranular gap,while the less primary phase grows from the remaining liquid phase,and the effects of both lead to a thicker film that separated by grains,decreasing the stress of crack appears,thereby increasing the hot-tearing susceptibility of the alloy.Then,the effects of Zr and Cr content on the mechanical properties and microstructure of the alloy were investigated.It was shown that as for homogenized and non-homogenized alloy during the casting state,the elongation of the alloy changes insignificantly with the addition of Zr and Cr,the yield strength and tensile strength both increase first and then decrease or gradually increase with the increase of Zr and Cr contents.The addition of Zr and Cr elements can refine the recrystallized grains of the alloy.The grain size and the yield strength of the alloy conform to the Hall-Petch relationship.It was also found that Zr and Cr can affect the precipitation and recrystallization of the alloy.By increasing the amount of larger size primary phase and the content of solid solution element Mn before recrystallization annealing,it also promotes heterogeneous nucleation and increases precipitation which can pin the intragranular dislocation and prevent the recrystallized grains from further growing to refine grain during the recrystallization.Based on the comprehensive analysis of the hot-tearing susceptibility and mechanical properties of the experimental alloys,it was found that the two experimental alloys containing Zr0.42wt% and Cr0.20wt% had relatively high strength and ductility,smaller hot-cracking tendency.