Reduction of Liquid Clad Formation Due to Solid State Diffusion in Clad Brazing Sheet
- PDF / 1,287,794 Bytes
- 10 Pages / 593.972 x 792 pts Page_size
- 19 Downloads / 195 Views
BACKGROUND
WHILE the use of aluminum (Al) alloys has seen increasing adoption in a number of automotive applications in recent years, they have been used extensively in automotive thermal management systems for decades, largely replacing copper and brass systems.[1] Thermal management products are most commonly fabricated through the controlled atmosphere brazing process, where formed sheets are assembled in the required configuration and placed within a furnace, which has the required temperature profile preset and an inert gas atmosphere.[2] The individual components that are joined are formed from clad Al alloy sheets, which consist of two or more layers, depending on the application. A core layer, typically an AA3xxx or AA6xxx alloy, provides strength for the assembly, while the clad layer, which consists of a lower melting temperature silicon (Si)-rich AA4xxx alloy, is present on the surface of the core alloy.[2] During brazing, the assembly is heated to a peak temperature above the clad alloy eutectic temperature, causing a portion of the clad metal to begin to melt. If MICHAEL J. BENOIT, Ph.D. Candidate, MARK A. WHITNEY, Research Associate, and MARY A. WELLS, Professor, are with the Department of Mechanical and Mechatronics Engineering, University of Waterloo, 200 University Ave. W., Waterloo, ON, N2L 3G1, Canada. Contact e-mail: [email protected] SOOKY WINKLER, Manager, is with the Materials and Processing Engineering Group, Dana Canada Corporation, 656 Kerr St., Oakville, ON, L6K 3E4, Canada. Manuscript submitted June 23, 2016. Article published online September 6, 2016. METALLURGICAL AND MATERIALS TRANSACTIONS B
the peak temperature is above the clad alloy liquidus temperature, all of the clad alloy will melt. Upon cooling, the liquid clad remaining on the sheet surface solidifies to form the braze joint. With the increasing market adoption of hybrid and electric vehicles in recent years, there is a corresponding need to develop new heat exchanger designs for the battery systems used in these vehicles. Brazing sheets traditionally used to fabricate heat exchanger products have typically been on the order of 500 lm thick, with clad layers of 10 pct of the sheet thickness on either one or both sides of the sheet.[3–5] Low cost, high performing battery cooling technology has resulted in the use of reduced thickness clad sheet with thicknesses on the order of 200 lm, with a correspondingly thinner clad layer of around 20 lm;[6,7] however, the room temperature forming limits of the reduced thickness sheets can be exceeded for some heat exchanger designs.[2] Recently it has been demonstrated that warm forming, where sheets are heated up to 573 K (300 C) during forming, can increase forming limits and reduce springback issues in clad brazing sheet.[8,9] The effect of warm forming on subsequent brazeability of clad brazing sheets however, has not been studied. The formation of high integrity braze joints requires sufficient liquid clad to be present at the joint location upon cooling from the brazing temperature.
Data Loading...
