The Research On The Second Phase Crushing Mechanics During Semi-solid Processing And The Properties Of Ferro-silicon-aluminium Alloy

Fining silicon and iron-rich phase is an effectively way to improve Al-Si-Fe alloy's performance.Therefore,in the thesis the semi-solid formation technology is adopted to prepare the Al-20Si-5Fe-3Mn-4Cu-lMg alloy,and the second phase crushing mechanics of Al-20Si-5Fe-3Mn-4Cu-1Mg alloy is analyzed systematically during semi-solid processing and its mechanical properties are also investigated.The strain in the alloy is simulated during semi-solid processing by analyzing stress state of the second phases.The results indicate that: both strain and extrusion ratios are in direct proportion to crushing stress,while temperature is in inverse proportion to crushing stress.The more D-value of stress area s₁ and s₃ is,the more crushing stress.The second phases inundeformed area is hardly crushed;the majority of the second phases in deformed area are mainly crushed to banding phases,and part of them grain phases.The needle and lathe-shaped second phases in slow flow area can be crushed many times.In the same time,edge angle of cubic phases become smooth.Only a few second phases in fixed diameter area are crushed. The simulation results indicate that: strain occurs mainly in deformed area and slow flow area;Small strain occurs in the top of the fixed diameter area;there is no strain occurs in undeformed area.The structure of Al-20Si-5Fe-3Mn-4Cu-lMg alloy is changed obviously after semi-solid processing.Coarse tabular and needle-like primary phases are replaced by round grainy phases,whose grain size is reduced largely. Eutectic structure also becomes finer and more even. The bigger extrusion ratio is,the finer both microstructure and the second phases are.It is the same case with temperature decreasing.It is in accord with simulation results.Mechanical properties of Al-20Si-5Fe-3Mn-4Cu-lMg alloy are highly increased by semi-solid processing.Ultimate tensile strength is 239.6Mpa,which 117.4% is improved than casting alloy.The value of extensibility reaches 2.0%,which is 3 times than casting alloy.With the increasing of extrusion ratio,both tensile strength and extensibility are improved.In elevated temperature,the bigger extrusion ratio is,the less weight loss is with no lubricant.Under the same condition, weight loss of the alloy,whose extrusion ration is 10:1, is just 30.78% than which of 390 alloy after 70min.Generally speaking,in elevated temperature, weight losses of Al-20Si-5Fe-3Mn-4Cu-lMg alloy with the three extrusion ration are rather small with lubricant.But the value of the alloy with extrusion ration 6:1 is the biggest among three kinds.The weight loss of the alloy with the extrusion ration 10:1 is 1.77mgjust 3.09% of 390 alloy.