Interface evolution and bond strength when diffusion bonding materials with stable oxide films

Abstract

The effects of stable surface oxides on the interface morphologies and strengths of aluminium diffusion bonds are reviewed. Previous approaches, proposed to overcome problems with surface oxides when joining aluminium alloys and composites, are described and compared for both solid-state diffusion bonding and conventional transient liquid-phase diffusion bonding. Non-conventional joining methods, particularly the new method of temperature-gradient transient liquid-phase diffusion bonding and its capability of producing high-strength bonds reliably, also are considered.

Identification of a friction model for the bearing channel of hot aluminium extrusion dies by using ball-on-disc tests

“…The plowing and shear friction have to be discriminated by means of FEM simulations [20,21] or theoretical analysis [24,32], and only the shear component of apparent friction representing the real friction between the two mating materials should be used in the FE simulations of metal forming operations as boundary conditions [20,21]. However, when the material combination of soft pin and 9 hard disc is used, the friction coefficients obtained from the tests are mainly attributed to the shearing (adhesive) friction.…”

“…The hardened H11 steel was selected as the mating material, which was the same material as that of extrusion dies. The tests were carried out under a constant normal load of 6 N at 350, 400, 450 and 500°C [24]. In order to achieve a high contact pressure between the mating materials, short sliding distance ball-on-disc tests were employed to represent the friction condition of the bearing channel of the hot aluminium extrusion process.…”

“…A previously developed model being able to characterize the evolution of contact interface during high-temperature ball-on-disc tests 10 was used to determine the mean friction stresses at different temperatures [24], which will be used for friction modelling in this research. Figure 1 shows the forces acting on an elemental area during ball-on-disc testing, which are given in Equation (1).…”

“…The bonding strength decreases with increasing temperature, due to the decrease of the strength of adhesive joints with increasing temperatures, and the bonding strength drops to zero at the melting temperature of AA7475 (Equation 6). The friction stresses obtained from short sliding distance ball-on-disc tests, details found in [24], were used to determine the constants of the model, by fitting the outputs of the model with the stresstemperature curve obtained from ball-on-disc tests. Table 1 lists the determined material constants.…”

“…In the past, tribological tests (pin/ballon-disc tests) have been employed to identify the friction coefficients for metal cutting 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 5 process [19][20][21][22]. Recently, the first attempt to determine the friction coefficient for hot aluminium extrusion process by using ball/pin-on-disc tests has been conducted [23,24].…”