Study of the Coarse Blocky Compounds in the As-cast 7075 Aluminium Alloys Containing Rare Earth Elements

摘要

The coarse blocky compounds in the as-cast 7075 aluminium alloys containing rare earth elements, neodymium, cerium or mischmetal were investigated by means of transmission electron microscope with EDX and scanning electron microscope. The blocky compounds in these alloys were identified as rare earth compounds, (Cr, Ti)_2RE(Al, X)_(20)(X is magnesium, copper and zinc), body-centred cubic, with 184 atoms to the unit cell, lattice parameter 1.453～1.458 nm, Vickers hardness 4000～5600 MPa and calculated density 3400 kg/m~3. The results show that the amount of blocky compounds in the alloys decreases with decreasing of Ti and Cr content or with increasing of cooling rate during solidification.