The Effect of Receiver Pressure on the Observed Flow Pattern in the Hydrostatic Extrusion of Bimetal Rods

An experimental study was conducted to determine the acceptable combinations of process variables for the production of a niobium-titanium superconducting alloy in a pure aluminum matrix by hydrostatic extrusion. Conditions for sound flow and defective flow are shown on plots of percent reduction in area versus die semicone angle. The superconductor used was a 56 percent Nb-44 percent Ti alloy surrounded by a matrix of 99.995 percent pure aluminum. The study was performed in three phases. Single-core billets were extruded into atmospheric pressure with reduction in area, die semicone angle, and the ratio of the volumes of the two phases being varied. Single-core billets were extruded into receiver pressure with reduction in area and die semicone angle being varied. Billets with three cores were extruded with reduction in area, die semicone angle, friction, and receiver pressure being varied. In all cases there was a light mechanical bond between the two materials produced by interference fitting of the cores into drilled holes. Experimental results showed that increasing the receiver pressure increases the range of acceptable process variables to produce sound flow. Although it was possible to produce sound flow, the results were not always consistent and repeatable. This is largely due to the great difference in strength between the soft aluminum and the hard superconductor and the difficulty in accurately controlling the bond strength. It is expected that the beneficial effect of receiver pressure will be even more pronounced with a tighter control on bonding.