Microstructure And Properties Of Al-5Ti-1B Alloy Processed By ECAP Severe Plastic Deformation

Al-5Ti-1B alloy is widely used grain refiner in aluminum processing field.To improve the comprehensive properties of cast aluminum alloy,grain refinement by the addition of Al-5Ti-1B alloy has become a common practice.The refining performance of Al-5Ti-1B alloy is determined by the second phase characteristics.Al-5Ti-1B alloy with different second phase size can processed by ECAP(Equal Channel Angular Processing)process.Nowadays,some researches have been done aiming at second phase broken mechanism in ECAP,the broken mechanism,however,was still not clear.The broken mechanism of second phase need to be finger out,and effect of ECAP process on refining performance of Al-5Ti-1B alloy is not clear.This paper was designed to solve above problems.In this paper the self-prepared Al-5Ti-1B alloy was used as raw material for multi-pass ECAP,and the microstructure and mechanical properties of Al-5Ti-1B alloy were studied.Grain refining mechanism was analyzed by observing grain evolution of Al-5Ti-1B alloy during multi-pass ECAP.The second phase broken mechanism during multi-pass ECAP was analyzed by observing TiAl3 and TiB2 evolution of morphology,size and distribution.Al-5Ti-1B alloy with different second phase size were made by ECAP,and their refining property and mechanical property change were analyzed.The major conclusions are as follows:(1)The grain refinement mechanism in Al-5Ti-1B alloy during multi-pass ECAP was obtained.The fraction of LAGBs(Low Angle Grain Boundaries)in Al-5Ti-1B alloy was rapidly increased at the beginning of ECAP process.Then,LAGBs transformed into HAGBs(High Angle Grain Boundaries)with the increase of deformation,which indicated that new grains appeared and the average grain size was decreased.And the fraction of LAGBs decreased since its transformational rate was large than its generation rate.The average grain size of Al-5Ti-1B alloy was rapidly decreased from 100.7?m to 15 ?m after 3 ECAP passes,then the average grain size was 8.6 ?m after 6 ECAP passes.Finally,the average grain size of alloy was about 8.1?8.6 ?m.(2)The evolution mechanisms of TiAl3 and TiB2 during multi-pass ECAP process were obtained.TiAl3 in Al-5Ti-1B alloy was obviously broken after ECAP.There are two position where creaks appear,and the cracks initiated from the inside TiAl3 and he edge of TiAl3.Then,TiAl3 was broken because small cracks expanded and combined with other cracks.The distribution of TiAl3 and TiB2 appeared obvious orientation after 4 ECAP passes,and the included angle of second phase orientation and ECAP direction was 41°.(3)Effects of ECAP pass on refining performance of Al-5Ti-1B alloy were achieved.The refining performance of Al-5Ti-1B alloy was increased with the increasing of ECAP pass during 1?8 passes,however,the refining performance was decreased after 9 and 10 ECAP passes.Effectual time of Al-5Ti-1B alloy was decreased with the increasing of ECAP pass during 1?7 passes,and the effectual time was increased with the increasing of ECAP passes after 8 passes.The refining performance of Al-5Ti-1B alloy after 1?7 ECAP passes would not attenuate in 30 min.The refining performance of as-cast Al-5Ti-1B alloy and Al-5Ti-1B alloy after 8?10 ECAP passes appeared attenuation decreased within 30 min.(4)Effects of ECAP process on mechanical properties of Al-5Ti-1B alloy were achieved.The UTS(Ultimate Tensile Strength),elongation and hardness of Al-5Ti-1B alloy after 10 ECAP passes were was 218 MPa,20.6%and 125 HV,respectively.The UTS and hardness were obvious increased,and the elongation was decreased.The UTS and elongation of alloy changed rapidly during 1?4 ECAP passes.Then,the UTS was slowly increased and the elongation was stable after 4 ECAP passes.The hardness of alloy increased rapidly during 1?2 ECAP passes,and increased slowly during 3?10 ECAP passes.