Woohyun Song

Diode laser brazing of aluminium alloy to steels with aluminium filler metal

Abstract Diode laser brazing of aluminium alloy (A5052) to interstitial free steel (IF steel) or type 304 stainless steel (SUS304) was conducted using aluminium filler metal (BA4047) with Nocolock flux. The processing parameters of laser power, wire feed rate and travel speed were varied. The strength of lap joints of A5052 on steels was evaluated by tensile shear test. The joint strength of A5052/steels was increased with increasing laser power and reached the maximum strength, more than approximately 80% of the A5052 base metal strength, at a laser power of 1300 W. Voids and incomplete penetration of filler metal were observed at the A5052/braze layer interface when the laser power was below 1100 W. The Fe–Al intermetallic compounds were formed at the steel/braze layer interfaces and grew drastically when the laser power exceeded 1300 W. Superior brazability of A5052/steels was found at brazing conditions corresponding to a temperature of filler metal droplet of 1050–1250 K.

Laser brazing of alloy 600 with precious filler metals

Abstract The diode laser brazing of Ni base heat resistant alloy with precious filler metals has been conducted using the tandem beam for preheating and brazing. A couple of 1 mm thick plates of alloy 600 (Inconel 600) were butt brazed using Au–18Ni, Ag–10Pd and Ag–21Cu–25Pd filler metals of 0·5 mm diameter with a brazing flux. Sound butt joints which were free from brazing defects such as porosity and lack of penetration could be obtained at brazing clearances of 0·1–1·5 mm. The tensile strength of the braze joint produced using Ag–Pd filler metal increased with decreasing brazing clearance and reached ∼70% of the base metal strength at a brazing clearance of 0·1 mm while those obtained by using Au–Ni and Ag–Cu–Pd filler metals were comparable with the base metal strength at any clearances between 0·1 and 1·5 mm. The laser brazing technique could be successfully applied to the brazing of Ni base superalloy to attain a joint with high performance and reliability.

Hot cracking in laser braze joint of high strength stainless steel using gold brazing filler metal – prevention of hot cracking by controlling thermal cycle

Abstract The hot cracking behaviour in the diode laser braze joint of 13Cr–4Ni stainless steel using Au–18Ni, Ag–10Pd and Ag–21Cu–25Pd filler metals has been investigated. The types of joint investigated were the T fillet joint and the L fillet joint which simulated the second braze bead in the T fillet joint. Tandem beam brazing was also carried out in order to prevent the hot cracking by post-heating treatment with a trailing beam. A centreline crack, characterised as a ductility dip crack, occurred in the second braze bead of the T fillet joint using Au–Ni filler metal. On the other hand, no cracks occurred in either the first or the second braze bead in T fillet braze joints using Ag–Pd and Ag–Cu–Pd filler metals. The hot cracking susceptibility of the Au–Ni braze metal was evaluated by the spot Varestraint test. Most of the cracks observed in the spot Varestraint test specimen were also characterised as ductility dip cracks, and the susceptibility to such cracking increased with increasing the augmented strain. The ductility dip temperature range (DTR) was estimated from the crack position and length to be 1000–1250 K at strains over 0·4%. Numerical analyses of the thermal stress and strain revealed that the plastic strain–temperature curve intersected the DTR in the single beam brazing, but did not intersect the DTR with post-heating during the laser brazing. The effect of post-heating on the crack prevention was verified by tandem beam brazing of L fillet joint with a trailing beam. No cracks occurred in the braze bead made with a trailing beam at laser powers of 200–300 W. The authors concluded that hot cracking in the Au–Ni braze metal could be successfully prevented by controlling the thermal cycle during the laser brazing process.

Tandem laser brazing of heat-resistant alloys using precious filler metals

The diode laser brazing of heat-resistant alloys with precious filler metals has been conducted using the tandem beam which consisted of preheating beam and main brazing beam. The 1mm thick plates of Inconel 600 and A286 alloys were butt-brazed using the 0.5mm diameter Au-18%Ni, Ag-10%Pd and Ag-21%Cu-25%Pd filler metals with a brazing flux. The processing parameters of the tandem laser powers and the brazing clearance were varied. The sound butt joints could be obtained by using the tandem beam with the laser powers of 400-500W/100-150W even at the narrow gap brazing below 0.2mm wide where the melted filler metal did not infiltrate completely into the joint gap by only using the main brazing beam (single beam brazing). Fracture strength of braze joint using Ag-Pd filler metal increased with decreasing the brazing clearance and attained about 70% of the base metal strength at the brazing clearance of 0.1mm, while those using Au-Ni and Ag-Cu-Pd filler metals were comparable to the base metal strength at any brazing clearance between 0.1-1.5mm. The preheating effect during the tandem beam brazing resulted in the superior brazability in the situation from the narrow gap to the wide gap brazing because of the improvement in wettability, spreadability of melted filler metal and the erosion resistance of base metal by depressing the extremely rapid cooling rate and steep temperature distribution in the base metal.The diode laser brazing of heat-resistant alloys with precious filler metals has been conducted using the tandem beam which consisted of preheating beam and main brazing beam. The 1mm thick plates of Inconel 600 and A286 alloys were butt-brazed using the 0.5mm diameter Au-18%Ni, Ag-10%Pd and Ag-21%Cu-25%Pd filler metals with a brazing flux. The processing parameters of the tandem laser powers and the brazing clearance were varied. The sound butt joints could be obtained by using the tandem beam with the laser powers of 400-500W/100-150W even at the narrow gap brazing below 0.2mm wide where the melted filler metal did not infiltrate completely into the joint gap by only using the main brazing beam (single beam brazing). Fracture strength of braze joint using Ag-Pd filler metal increased with decreasing the brazing clearance and attained about 70% of the base metal strength at the brazing clearance of 0.1mm, while those using Au-Ni and Ag-Cu-Pd filler metals were comparable to the base metal strength at any...