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

Abstract

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.

A Fragmentation Criterion for the Interface of a Hydrostatic Extruded Al-Mg-Compound

“…The lengths of the gaps are also summed up to l G T in Equation (3) and used to calculate the percentage of gaps on the interface p G after channel compression according to Equation (4). In contrast to ε F , the variable p G is only based on dimensions measured at the deformed cross section and is not subjected to any assumptions like l 0 :…”

“…This offers the potential to comply with the requirement of weight saving in several fields of industry, e.g., automotive [1] and aeronautical. Therefore, several investigations have been done since the early 1970s on the co-extrusion process with different material combinations [2][3][4].…”

Physical and Numerical Analysis of Extrusion Process for Production of Bimetallic Tubes

“…An increase in the ratio of only 25 to 50% will decrease the operating window in which successful extrusion may occur. 2,4,9,22,24 When the ratio becomes higher, extremely nonuniform flow occurs, and the material does not concurrently extrude or bond together. Figure 3.5 is a schematic representation of a flow net located at the center of a billet during extrusion.…”

“…4,22 Shaving, also known as back flow or sleeve ironing, occurs when very low extrusion ratios are used; these are more prevalent with a hard core material and in dies with a large cone angle. 4,22,24 In this case, the core material does not deform, or deforms only slightly, preventing the sleeve material from entering the die orifice. Due to conservation of volume, the sleeve material flows backwards (expedited by its lower flow stress).…”

“…21 As core diameter decreases, the effect of R is less severe, and successful extrusion can be carried out at relatively high R values. 22 One of the strongest influences on concurrent flow and failure of the extruded material is the interfacial friction m i or interface bond strength. As has been shown in the work by Avitzur 9 as well as others, 23 the higher the friction between the materials/bond strength, the lower the occurrence of core failure.…”