B. P. Serole, SEROLE . EXPERT ., PEYRINS, France

Summary: Surprising mechanical characteristics have been obtained through gas atomisation of aluminium alloys . Basis . Two aluminium alloys, used in the car industry , have been selected : AS22UNK is a hypersilicied alloy in the range of standard piston materials . The typical analysis of the used 20 kg ingots is : Element : Al Si Fe Cu Mn Mg Ni Co W% Bal. 20.4 0.30 1.40 0.51 1.06 1.27 1.01 The other is the Al Fe 8 Mo used for forged connecting rods . Some tests have been made for checking with up to 30 and 35 W% Si , Al Li .... The AS22 ingots show silicon crystals of some mm to some cm . A good gas atomisation with a cooling rate of 10^3 °K/Sec. gives silicon crystals of 100 µm . A fast cooling one with a rate of 10^6 , 5 µm . The melt spining ribons show an amorphous side , white and X Ray flat . The other side is grey . Atomisation . We used supersonic close coupled nozzles surounding a newtonian 2 mm dia. liquid alloy stream at 800 °c . It correspnds to about 80 kg/hour . The nozzle delivers an argon flow between : For 7 Bars at 293 °K to O.860 Bars the exhaust is at Mach 1.96 409 m/s 131 °K For 60 Bars at 293 °K to 0.860 Bars it is Mach 3.40 491 m/s 59 °K Liquid ?. The cooling rate was roughly estimated by the exhaust speed and the flying distance necessary to see the grains bouncing on a 304L rod instead of making a cake . The powder stream still liquid was sucked and pushed thru a dynamic 'needle hole' some 10 cm below the nozzle . There the conditions were between a liquid and solid contact . We named the grains ' white white' and the X Rays were flat The powder was put in an Al Mg container under vacuum and isostatically extruded in 25 mm dia . 1350 mm long rods on a 1 000 tons hydraoulic press . Probably itshould have been better to use a shock wawe fast forge such as the one used for AFS 350 kg ingots which has the same temperature problems . Results . They have been exciting . In the best annealing conditions - 340 °c - the hardness has 250 HV ( 140 kg/mm2 ) with an elongation near to 10 % . Temporary conclusions . This work needs to be achieved and some points confirmed but alraedy two conclusions can been sure . The gas atomisation is an industrial and cheap way. The mechanical strength looks like the one of a mar aging with a density of 2.6 g/cm3 instead of 7.8 But it raises more questions than it solved : The process seems to work with most of the aluminium alloys and probably with everything being atomised , even the inconels . Why not ? We used supersonic nozzles with argon but the quenching device could be fed with plasma nozzles giving nano powders. The argon atomised aluminium we made explodes just by looking at air ( if not passivated) what about a nano and amorphous ? We have forged and rolled AFS ingots of 350 kg and prepared the 2 tons . But are they not already obsolete if we have at our hand the nano and amorphous version ? When annealed at 400 °c it appeared in the Al Si 22 tiny stars looking like nothing . Is this structure interesting ? Is it worth to atomise again Al + whiskers with this technology ?.. Patents Line 1 Atomisation and plasma Extended . Line 2 Shock wave forge . Extended .