The Effect Of Trace Cr,Ti And Fe On The Microstructure And Properties Of 6061 Alloys

6061 is a kind of 6XXX alloys,which are widely used.Although the role of trace elements in the alloyhas been studied extensively both athome and abroad,the work that the influence of trace Cr,Ti,Fe elements on thehigh purity 6061 alloy based on the main elementshas been seldom reported Therefore,the effect of trace Cr,Ti,Fe elements designed and added to casthigh purity 6061 aluminum alloy on its microstructure and properties was explored with the optical microscope(OM),scanning electron microscopy(SEM)and spectrum analyzer,differential scanning calorimetry analysis(DSC),conductivity,mechanical properties,solid solution and aging treatment,annealing recrystallization test in this paper.The main conclusions can be drawn as following:(1)Detected by the glow discharge mass spectrometry(GDMDS)analysising 69 elements,the content of 66 impurity elements except Mg,Si,Cu in the 6061 alloy casted withhigh purity graphite crucible and tools is less than 0.0035%(wt%).Compared with 6061 alloy casted withhigh purity graphite crucible,the content of Si in the 6061 alloy casted with clay graphite crucible and the same tools increases slightly.(2)0.23%Cr?0.05%Ti?and 0.5%Fe added inhigh purity 6061 alloy can refine its casting microstructure,and the effect shows as following:0.05%Ti>0.5%Fe>0.23%Cr.(3)On the matrix and grain boundary of the casting microstructure inhigh purity 6061 alloy,the phase containing Cr(often including Cu),less than 5 ?m,appears,while the phase containing Ti is not found.Adding 0.5%Fe alone,containing Fe phase(approximatly?-Al8Fe2Si)and acicular phase(composition approximatly ?-Al9Fe2Si2)perpendicular to the the grain boundary appear When Cr,Ti,Fe are added in 6061 alloy at the same time,the acicular ?-Al9Fe2S disappears.(4)The burnt temperature of semi-continuous castinghigh purity of 6061 alloy is about 577?.With 530? × 34h homogenization treatment,?(Mg2Si)phase and phases containing Cu,Cr can dissolve into the matrix.Phases containing Fe,Si occur phases transition:?-Al9Fe2Si2?a-Al8Fe2Si,and become irregular granular form.(5)With solid solution treatment in the interval of 490??550?,the strength of 6061 alloy improves as the solid solution treatment temperature increases,while elongation decreases gradually.However adding Cr,Ti,Fe elements,elongation of 6061 alloy remains unchanged.According different solid solution time at 540 ? the strength ofhigh purity 6061 alloy without Cr,Ti,Fe elements rises firstly,then falls and occurs a maximum value(30minutes),while the strength of 6061 alloy added Cr,Ti,Fe elements extends monotonically.(6)With the aging time gradually extends in the interval of 6?16h at 170 ? the intensity of 6061 alloy increases monotonously,while elongation decreases except the one added Cr,Ti,Fe elements.The optimal solid solution and aging progress of 6061 alloy added Cr,Ti,Fe is shown as following:550?×1h solid solution treatment(water quenching)and 173 ?×10h aging treatment,and its mechinal properities improves to:? b=372MPa,? 0.2=337MPa,? ?15%.(7)When 0.23%Cr,0.05%Ti,or 0.5%Fe are added in the plastic deformation 6061 alloy,The recrystallization(improving recrystallization temperature)can be restained,the ability to inhibit recrystallization can be shown as:0.23%Cr>0.5%Fe>0.5%Ti.