Investigation Of Dispersoids And Properties At High Temperature Of Al-Mn Alloys

At present,aluminum alloys are extensively used in the fields of weapons,ships,aviations,aerospaces,automobiles and heat exchangers,the comprehensive properties of aluminum alloy at room temperature have been extensively studied.However,the development of heat-resistant aluminum alloys used at high temperatures lacked of new ideas.The idea of this study is to make the dispersoids in the aluminum alloys as the high temperature strengthening phase and dispersoids are effectively matched with the crystal phases.Therefore,the properties of heat-resistant aluminum alloys are further improved.The aim of study is to explore a way to improve the number and density of dispersoids through alloying and proper pretreatment based on Al-Mn alloys which form more dispersoids.Consequently,it is possible to lay the foundation of developing a new heat-resistant aluminum alloy through effectively match of dispersoids,crystal phases and the dispersoids as high temperature strengthening phase.The results show that:(1)During semi-continuous casting,a large number of coarse crystal phases containing Mn,Cr and V with size of 30?150?m appeared in Al-4Mn-0.15V-0.22Cr alloy.The distribution of dendrites is not obvious in this alloy.Only a few number of excess phases with a size of less than 10 ?m appeared on the matrix.After the homogenization heat treatment,crystal phases containing Mn,Cr and V altered little,a large number of dispersoids precipitated in the alloy.Coarse primary crystal phases was partially crushed and distributed along the rolling direction.Structure altered little after annealing at 300?.(2)A large number of dendrites with(Al-Al2Cu)eutectic appeared when add 4%Cu into Al-4Mn alloy.In addition,coarse bulk crystal phase transformed into needle rod-like coarse crystal phase with size of 100-250 ?m.Fe participated in the formation of coarse crystal phases containing Mn,Cr and V but have an implicit influence on its morphologies when adding alloy elements Fe and Ni into Al-4Mn-4Cu alloy,dendrites with(Al-Al2Cu)eutectic and phases containing Fe and Ni appeared.After homogenization heat treatment,partily(Al-Al2Cu)eutectic dissolved into the matrix,partily(Al-Al2Cu)eutectic and phases containing Fe and Ni formed discrete excess phases with size of 1?2 ?m at the position of the original dendrite,partily formed new phases containing Cu surrounding coarse crystal phases In addition,rod-like dispersoids which the size of less than than 0.5 ?m and density higher than Al-4Mn alloy precipitated in the alloy.(3)The element Si not only involved in the formation of coarse crystal phase and transformed it into long needle-like shape,but also formed a large amount of eutectic products containing Si and Mn.After homogenization heat treatment,coarse needle-like crystal phases changed little,eutectic products containing Si and Mn spheroidized and further roughened.Fe not only involved in the formation of coarse crystal phase and transformed it into long needle-like shape,but also formed a large amount of eutectic products containing Si and Mn.After homogenization heat treatment,Coarse crystal phases changed little,the eutectic products evolved into rod-like and spherical phases containing Mn,Fe,Si and Ni with the size of about 5?10 ?m,a lage number of dispersoids with size of under 0.3 pm appeared.(4)Cr not only participated in the formation of coarse crystal phases but also involved in the formation coarse dispersoids,V only participated in the formation of coarse crystal phases when adding a small amount of Cr and V into Al-4Mn alloy.(5)The coarse primary crystal phases was partially crushed and distributed along the rolling direction,dispersoids were increased obviously through adding 4%Cu into Al-4Mn(trace Cr and V)after hot rolling.Higher density dispersoids of larger size of containing Mn,Cu and smaller size containing Cu appeared after final heat treatment.(6)The coarse primary crystal phase was crushed with shape of long rod-like and distributed on the alloy matrix through adding 3%Si into Al-4Mn(trace Cr and V)after hot rolling.The microstructure changed little after annealing at 300?.Adding Fe and Ni into Al-4Mn-3Si alloy,the coarse primary crystal phase containing Mn,Si and Fe was not obviously shredded and the distribution of dispersoids was not uniformly after hot-rolling.(7)The dispersoids containing Mn and Cr were refined and their density was increased by pre-treatment of 250?×72h before the homogenization heat treatment.(8)During semi-continuous casting,coarse crystal phase do not appeared but dendrite network consisting of bulk and lamellar Al9FeNi phases with size of 3?5?m and phases containing Mg and Cu with size of 1?m appeared in 2618 alloy.After homogenization heat treatment,phases containing Mg and Cu dissolved into the matrix,spheroidal and rod-like Al9FeNi phases with size of about 1?3 ?m remained,phases containing Cu and Fe were partially spheroidized.After hot rolling,excess phases were more fine and well-distributed.After final heat treatment,the size of spherical phases containing Fe and Ni was about 1?m and the size of rod-like phases containing Cu,Fe and Ni was about 1?2?m.(9)At room temperature,the strength of four alloys from high to low was as follows:2618 alloy,Al-4Mn-0.15V-0.22Cr alloy,3003 alloy Al-4Mn-3Si-1.2Fe-1.2Ni alloy.The extensility of four alloys from high to flow was as follows:3003 alloy Al-4Mn-0.15V-0.22Cr alloy,Al-4Mn-3Si-1.2Fe-1.2Ni alloy,2618 alloy.At 250?,the strength of six alloys from high to low was as follows:2618 alloy,Al-4Mn-4Cu-0.15V-0.22Cr alloy,Al-4Mn-0.15V-0.22 Cr alloy,Al-4Mn-3Si-0.15V-0.22Cr alloy,3003 alloy,Al-4Mn-3Si-1.2Fe-1.2Ni alloy.The extensility of six alloys from high to flow was as follows:Al-4Mn-0.15V-0.22Cr alloy,3003 alloy,2618 alloy,Al-4Mn-4Cu-0.15V-0.22Cr alloy,Al-4Mn-3Si-1.2Fe-1.2Ni alloy,Al-4Mn3Si-0.15V-0.22Cr alloy.