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Effect of NOCOLOK® flux dry-off temperature on mechanical properties of brazed joint for automotive aluminum-based heat exchangers

The drying temperature of the flux at a normal atmosphere has a crucial role in brazing quality in automotive aluminum-based heat exchangers. Throughout this research, NOCOLOK® flux consists of two phases of K2AlF5.H2O and KAlF4 with a melting point around 580 °C was used. A flux slurry was applied on the base metal and dried at 220, 300 and 380 °C in air. The mechanical assessment revealed that when flux dried at 300 °C, the joint withstand maximum shear stress of 44 MPa with complete bonding. At 220 °C and 380 °C, joint shear stresses are 34 MPa, 30 MPa respectively. 380 °C dry-off temperature under nitrogen gas improved shear strength to 39 MPa. Taking dry-off temperature as 300 °C the number of defective heat exchangers was reduced from 3.2% to 0.6% every week.