Microstructure Evolution And Formation Mechanism Of Al/Al And Ti/Al Interfaces During Ultrasonic Consolidation

Ultrasonic consolidation(UC)is an advanced additive manufacturing technique that utilizes ultrasonic energy and normal force to rapidly join thin similar/dissimilar metal tapes into solid parts in a layer accumulating manner.However,due to the lack of knowledge to effect of the ultrasonic energy on metal materials,the interface formation mechanism of ultrasonic consolidation technique has not been unified till now.In this dissertation,the interface formation mechanism of Al/Al and Ti/Al similar/dissimilar metals during UC process has been thoroughly investigated.Moreover,to overcome the difficulties in Ti/Al interface formation,a newly-developed Electropulsing Assisted Ultrasonic Consolidation(EPA UC)technique has been firstly conducted and investigated according to the effect of electropulsing energy as electroplastic.In this work,the effect of electropulsing current density on the bond quality,microstructure and texture evolution,and atom diffusion etc.during the Al/Al and Ti/Al EPA UC process has been thoroughly investigated.Through the above researches,the results are obtained as follows:During the Al/Al ultrasonic consolidation process,the increase in ultrasonic amplitude and normal force can both effectively improve the bond quality.However,there are two different parameter thresholds that can induce the decreasing in bond quality.When the normal force is lower than 1000 N,the LWD maintains at an extremely low level and not affected by the variation of ultrasonic amplitude.When the ultrasonic amplitude is higher than 35μm,the maximum peeling load decreases with increasing normal force.Thus,the optimum parameters for the Al/Al ultrasonic consolidation process are between the range of 25μm～35μm ultrasonic amplitude and 1000N～1600N normal force.The obtained results indicated that in the slip phase dominated bond formation process,the recrystallized grains are much fewer than the stick phase dominated bond formation process.In the slip phase dominated bond formation process,the texture evolution path is{112}<111>→{100}<110>,and in the stick phased dominated bond formation process,the texture evolution path is {112}<111>→{100}<110>→{110}<112>.On the other hand,with the cyclic loading of ultrasonic energy during Al/Al ultrasonic consolidation process,dynamic recovery was found to take place at the bulk regions in the ultrasonically consolidated Al/Al samples.Under the low ultrasonic energy state,<110> fiber initiated within the bulk regions of Al/Al UC samples.With increasing ultrasonic energy input,the <111>fiber dominated due to which had more slip directions.The dynamic recrystallization took place at the bulk region with the increasing ultrasonic energy loading times,in which process the texture evolution path is{112}<111>→<110>∥VD→<111>∥VD→{100}<110>→{110}<112>.The increase in ultrasonic amplitude and normal force can both lead to the elevation of bond quality and atom diffusion distance during the pre-heated Ti/Al ultrasonic consolidation process.However,owing to the differences in the strength of Ti and Al,dynamic recrystallized grains were only observed at the interface region in Al side with {124}<211> R texture type,which showed obvious signs of abnormal grown tendency and grain reorientation under the influence of the temperature field.The TEM results revealed that the bond formation between Ti and Al during ultrasonic consolidation process is through the mutual diffusion of Ti and Al atoms,which is proven to be a metallurgical bonding interface.On the circumstance of the electropusling assisted ultrasonic consolidation process,the results indicated that the electropulsing current can effectively elevate the plastic deformation ability of Ti and Al foils.The EPA UC process makes the HA-LN Al/Al interface achieve a similar bond quality and microstructure as the bonded interface fabricated under the HA-HN single ultrasonic energy induced process.On the other hand,the Ti and Al foils have been successfully consolidated by this electropulsing assisted ultrasonic consolidation process at room temperature.The results showed that obvious plastic flow occurred at the Ti interface,which indicated an elevation in the atom diffusion ability at the Ti/Al interface region.The TEM results showed that,at the Ti/Al interface region,fine and equiaxed grains maintained at Al side according to the room temperature atmosphere.Furthermore,evident increase in Ti and Al atoms diffusion distance was also observed under the electropulsing assisted ultrasonic consolidation process.The diffusion distance of Ti and Al atoms under UPA UC process increases from 20 nm to 30 nm comparing to the traditional single ultrasonic energy induced UC process.