Fabrication Of Al Laminate Composites Via Accumulative Roll-bonding And Cryogenic Rolling And Their Performance Study

Al laminate composites have great development potential in the manufacture of lightweight structural parts.Rolling compound method is one of the most commonly used methods to prepare Al laminate composites.At present,the mature application methods include hot rolling,cold rolling,accumulative roll-bonding and so on.However,the mechanical properties of the materials prepared by these methods need to be further improved.Aluminum alloy has excellent plastic deformation ability in cryogenic environment,but the compound forming of Al laminate composites by cryorolling remains to be studied.Therefore,in order to further optimize the overall performance of these materials and broaden their application scope,this dissertation studies the variation rule of mechanical properties of Al laminate composites prepared by different rolling processes,and analyzes and discusses the mechanism of cryorolling in strength improvement.In order to reveal the effect of rolling processes on mechanical properties of Al laminate composites,series 1 aluminum alloy AA1050,non-aging strengthened aluminum alloy AA5052 and aging strengthened aluminum alloy AA6061 are selected as research objects.AA1050/AA5052 and AA1050/AA6061 Al laminate composites are prepared through several rolling processes,and the subsequent aging process of AA1050/AA6061 Al laminate composites is explored.The main results are as follows:（1）The reasonable rolling process for preparing AA1050/AA5052and AA1050/AA6061 laminate composites is established through the change rule of mechanical properties:three passes of accumulative roll-bonding+two passes cryorolling.After three passes of accumulative roll-bonding,the strength of AA1050/AA5052 and A1050/AA6061 laminate composites are 256±2 MPa and 236±1 MPa respectively.The mechanical properties of the Al laminate composites are reduced by further accumulative roll-bonding.However,the highest ultimate tensile strength of AA1050/AA5052 and A1050/AA6061 laminate composites obtained by cryogenic rolling are 284±1 MPa and 310±1 MPa,respectively.（2）The internal mechanism of performance evolution is revealed through microstructure analysis.According to the characterization of layered structure,the hard layer has obvious necking and fracture in the fourth and fifth passes of accumulative roll-bonding,which is due to the plastic instability caused by the different flow characteristics between the two components.In contrast,the layered structure of Al laminate composites after cryorolling is relatively flat,indicating that the deformation uniformity between the constituent layers has been significantly improved,which can also well explain the strength changes under different rolling conditions.In addition,through the analysis of SEM and TEM results,it is found that cryogenic rolling has significant advantages in improving interface bonding quality and refining grains.Another reason for the obvious improvement of the strength of Al laminate composites is that cryorolling can effectively inhibit the dynamic recovery,so that the accumulative dislocation density reaches a higher steady-state level,which plays an important role in further grain refinement.（3）The mechanical properties of AA1050/AA6061 laminate composites are optimized by low temperature aging.Under the four aging temperatures,the hardness values of AA1050/AA6061 laminate composites show a tortuous upward trend with the increase of aging time,and decreases slowly after reaching the peak aging.After aging at100℃/54 h,the maximum hardness value of the cryo-rolled sample is145.1±0.5 HV and the corresponding ultimate tensile strength value is328±1 MPa.The increase of ultimate tensile strength after peak aging can be attributed to the higher dislocation density accumulated by cryorolling.These dislocations can not only strengthen,but also provide more nucleation sites for the precipitation of Mg₂Si.Finally,AA1050/AA6061 Al laminate composites with excellent properties are obtained through compound rolling process and subsequent aging treatment.