In Situ Measurement of the Thermal Contact Resistance of an Al Lap Joint During Braze Processing

Abstract

A technique was developed, using a laser flash thermal diffusivity apparatus, to measure the thermal contact resistance, Rc, of an Al lap joint during braze processing. The method required a determination of the temperature dependence of the thermal diffusivity of the individual Al braze sheets, as well as a two-layer lap joint made from these sheets, under identical conditions. A two-layer modeling method was then used to analyze the above data to determine Rc for the lap joint as a function of processing temperature. This in situ analysis of Rc for a developing joint during brazing was able to distinguish both solid-state and liquid-phase reactions occurring at the faying surfaces of the joint. Consequently, it represents a powerful, new experimental tool that can be used to investigate the mechanisms of braze joint formation and the thermal properties of a joint as a function of processing condition. In the particular case of this study, the technique demonstrates that the use of a Ni-based fluxless brazing process to join aluminum (Al) sheets, reduced the Rc of the lap joint by 100-folds from 1.3 × 10−4 m2 K/W before brazing to 1.35 × 10−6 m2 K/W after brazing.