The Effect Of Local Loading Travelling Magnetic Field On The Solidification Defects And Properties Of Zl205A Alloys

ZL205A alloy with very large crystallization temperature range (89°C),solidifying by mushy mode, is easy to produce shrinkage defects duringsolidification, and it is still difficult to feed the casting even with a riser. Therefore,it is very crucial to take measures to improve or eliminate the defects for improvingthe quality and properties of ZL205A alloy castings. Travelling magnetic fielddensification technology can be used to solve the difficult problem of ZL205A alloynot easy to feed, because travelling magnetic field can produce electromagneticforce in molten metal and induce forced convection stirring, which can furtherdensify the solidification microstructure. In this work, ZL205A alloy was used asexperimental material. Travelling magnetic field inductors were developedaccording to its principle. The influence of travelling magnetic field direction onfeeding was investigated and then the effect of travelling magnetic field with certaindirection and intensity on feeding castings with different wall thickness wasresearched.In order to study the influence of travelling magnetic field direction onsolidification shrinkage defects, two sets of travelling magnetic field equipmentwith different connection mode were used, whose direction was that one is the sameas the direction of gravity and the other on the contrary. The study shows that whentravelling magnetic field direction coincides with the direction of gravity, moltenmetal is more largely squeezed along the travelling magnetic field direction as aresult of the existence of electromagnetic force, which increases the penetrationability between dendrite frames of molten metal, at the same time, the forcedconvection stirring effect induced by travelling magnetic field has an effect onbreaking dendrite frames and further decreases the feeding resistance, resulting inbetter feeding effects. When travelling magnetic field direction is opposite with thedirection of gravity, gravity is offset by electromagnetic forces to some extent, thefeeding effect is bad.The feeding ability of travelling magnetic field with certain intensity, whosedirection is the same as gravity, on castings with wall thickness7mm,20mm,30mm,respectively, was studied. Results show that travelling magnetic field can greatlyimprove solidification shrinkage defects under three different conditions, but theimprovement has its limit. When the casting wall thickness is less than20mm, thesolidification shrinkage defects can be completely eliminated. For the castings withwall thickness over20mm, the shrinkage defects can be improved but cannot be absolutely eliminated. Results also indicate that Cu will move in the Al matrix alongtravelling magnetic field direction because of the different conductivity betweenthem, and the θ(Al2Cu) phase at grain boundaries decreases, dissolving in the grains,which is good for heat treatment. At the same time, the strengthening phases, suchas Al3Ti, Al7V, Al3Zr, and so on, are refined. The castings fed by travelling magneticfield have less shrinkage cavities and porosities, higher tensile strength andelongation.