Effect Of Ce-Rich Rare Earth On Microstructure Evolution And Properties Of 5182 Aluminum Alloy

Due to its good tensile properties and formability,5182 aluminum alloy is used as an automobile inner lining and structural parts with complex shapes.In terms of modification of aluminum alloys,compared with other traditional modifiers,cerium-rich mischmetals can refine the grains of aluminum alloys and at the same time improve the morphology,size and distribution of the second phase in the alloy structure.However,there is still no systematic analysis of the mechanism of cerium-rich mischmetal's modification of aluminum alloy structure and the enhancement of performance.In this paper,the effect of cerium-rich mischmetal on the as-cast,homogenized and annealed,cold-rolled and recrystallized and annealed states of 5182 aluminum alloy was investigated.The mechanism of action of rare earth and the effect of different cold rolling processes on its effect,the strengthening mechanism of cerium-rich mischmetal on the properties of 5182 aluminum alloy was discussed,and the following conclusions were draw n:?1?Through the simulation of the equilibrium crystallization process by JMat Pro software,combined with DSC analysis and XRD and TEM phase identification,it is determined that the 5182-x MM aluminum alloy is mainly composed of?-Al,Mg₂Si,Al₆?Mn,Fe?and Al₄?Ce,La?phase composition.Using rich cerium rare earth under different cooling speed of metamorphic effect,deduce the metamorphic mechanism of rich cerium rare earth as the composition of supercooling mechanism,in the process of crystallization,rich cerium rare earth concentrati on on the solid liquid interface front,on the one hand,that causes the area composition is too cold,promote the secondary dendrite,three times of dendrite growth,when rich cerium rare earth content is 0.2%that the refining effect is best,the grain s ize from 90.96?m reduce to43.95?m,content increase will promote the Al₄?Ce,La?as soon as possible,the nucleation of abate refinement effect.On the other hand,it can reduce the efficiency of solute redistribution,inhibit the continuous network gr owth mode of Mg₂Si phase,and improve the solid solution quantity of Mg elements in the matrix.In addition,the cerium-rich mischmetal will also wrap around the primary Al₆?Mn,Fe?phase,inhibit the growth of the Al ₆?Mn,Fe?phase,and prevent Cr and Si elements from dissolving into the Al ₆?Mn,Fe?phase.Through the discussion of mechanical properties,it is determined that the strengthening mechanism of cerium-rich mischmetal on mechanical properties is mainly fine crystal strengthening and solid soluti on strengthening.?2?The structure evolution of 5182-x MM aluminum alloy after uniform annealing was observed and analyzed by polarizing microscope,XRD and SEM.Homogenization annealing has almost no change in the alloy grain size,and the advantage of ce rium-rich rare earth on?-Al grain refinement is still obvious.The Mg₂Si phase dissolves during the homogenization annealing process,causing the Mg₂Si phase network structure in the 5182-0.2MM and5182-0.4MM aluminum alloys to disappear completely;the A l₆?Mn,Fe?phase is basically not dissolved during the homogenization annealing process,but,Impurity elements Cr and Si in 5182 aluminum alloy failed to diffuse from Al₆?Mn,Fe?phase to?-Al lattice completely,the size of phase after homogenization annealing is larger,the hardness is higher;5182-0.2MM and The Ce and La in the 5182-0.4MM aluminum alloy fully diffuse from the Al₆?Mn,Fe?phase to the phase boundary,promoting the nucleation of the Al₄?Ce,La?phase at the edge of the Al ₆?Mn,Fe?phase,and the microhardness has seen an increase.?3?XRD,EBSD,SEM and TEM observations were used to study the effect of cerium-rich rare earth on the cold rolled structure of 5182 aluminum alloy,and the difference of the effects of cerium-rich mischmetal under different cold rolling processes was compared.After the primary cold rolling,the dislocation density increases with the increase of cerium-rich mischmetal content,the strengthening mechanism is mainly dislocation strengthening and grain boundary strengthening,the maximum stress is 454.3 MPa;after the secondary cold rolling,the best cerium-rich mischmetal content is 0.2%,the strengthening mechanism is mainly grain boundary strengthening,and the maximum stress is 443.3MPa.The difference in the effect of cerium-rich mischmetal under different cold rolling processes is mainly due to the fragment size after the Al ₄?Ce,La?phase is crushed.The work hardening degree after one cold rolling is large,and the Al ₄?Ce,La?phase is highly fragmented,The size of the fragment is uniform,the higher the content of cerium-rich mischmetal,the greater the number of fragment particles,which promotes the proliferation of dislocations;the degree of work hardening after secondary cold rolling is small,and th e degree of Al₄?Ce,La?phase fragmentation is low.The block size is not uniform,the higher the content of cerium-rich mischmetal,the larger the size;the large-size Al₄?Ce,La?phase will undergo a PSN effect under the effect of intermediate annealing,which reduces the dislocation density in the alloy.Therefore,for the secondary cold rolling,the content of cerium-rich mischmetal should be controlled below 0.2%to avoid the appearance of large-sized Al₄?Ce,La?phase.?4?According to the difference of recrystallization behavior of 5182aluminum alloy under different cold rolling processes,the effects of cerium-rich mischmetal and different cerium-rich mischmetal content on the recrystallization structure were analyzed.The results show that the nucleation mechanism of recrystallization in a cold rolling is the sub-nuclear growth nucleation mechanism.The small fragments formed after the Al ₄?Ce,La?phase breaks form the movement of grain boundaries and sub-grain boundaries during the recrystallization process.The hindrance promotes the production of more fine crystals after recrystallization.The average grain sizes of 5182,5182-0.2MM and 5182-0.4MM after recrys tallization were 10.40?m,8.21?m and 7.50?m,respectively.The nucleation mechanism of secondary cold rolling recrystallization is the nucleation mechanism of grain boundary protrusion.The size of the recrystallized grain depends on the driving force of recrystallization.The PSN caused by the large-size Al₄?Ce,La?phase in5182-0.4MM aluminum alloy The effect provides more nucleation positions for recrystallization,promotes the increase of the number of crystal nuclei in the initial recrystallization,a nd reduces the hindrance to the movement of grain boundaries and sub-grain boundaries.The number of coarse crystals after recrystallization is large.The average grain sizes of 5182,5182-0.2MM and 5182-0.4MM after recrystallization were 10.94?m,8.45?m and 11.38?m,respectively.?5?According to the comparison between the theoretical calculation of mechanical properties and the actual measurement,it is concluded that the strengthening mechanism of 5182-x MM aluminum alloy after recrystallization annealing is mainly fine grain strengthening.After a cold rolling recrystallization,the mechanical properties increase with the increase of cerium-rich mischmetal content.When 0.4%cerium-rich mischmetal is added,the tensile strength of the alloy increases by 7%,reached 342.7MPa;the yield strength increases by 19%,reached 206MPa;After recrystallization after secondary cold rolling,the best performance is achieved when the content of cerium-rich mischmetal is 0.2%,the tensile strength of the alloy is increa sed by 5%,reached 336.6MPa;the yield strength is increased by 12%,reached184MPa;the elongation is increased by 21%and reached 23.5%.