Microstructural control in an aluminum core alloy for brazing sheet applications
- PDF / 2,990,253 Bytes
- 8 Pages / 597 x 774 pts Page_size
- 77 Downloads / 200 Views
I.
INTRODUCTION
H E A T exchanger units for automotive engines were, until the 1970s, manufactured from copper and brass. It is only in the last 15 to 20 years that radiator producers have developed joining techniques suitable for aluminum, i . e . vacuum and flux brazing (NOCOLOK*), to *NOCOLOK is an Alcan patented process for the noncorrosive flux brazing of aluminum components.
utilize the lighter weight of aluminum alloys. Typically, the radiator is comprised of a fin and tube assembly for heat removal and top and bottom header plates onto which the tanks are attached (see Reference 1 for example). The radiator would then be brazed by controlled heating to, soaking at, and cooling from a temperature between 580 ~ and 610 ~ Joints are created by the flow of a molten layer formed by an A1-Si eutectic alloy that melts at 577 ~ during the brazing cycle. In service, the radiator is subjected to conditions that include mechanical loading, vibration, and salt water environments during winter driving conditions. The most critical component is the tube for which high heat transfer, good corrosion resistance, both internally and airside, and adequate burst strength are required. The development of aluminum alloys to meet the varied requirements has progressed as the usage of aluminum has increased. This article deals with the development of an alloy t2} that has enhanced airside corrosion behavior in combination with high strength to offer long life to radiator makers and hence car manufacturers. In terms of airside corrosion, which is usually at its most aggressive in salt water, conventional aluminum alloys like AA3003 or AA3005 are generally attacked G.J. M A R S H A L L , R . K . B O L I N G B R O K E , and A. G R A Y , Scientists, are with the Banbury Laboratories, Alcan International Limited, Banbury, Oxon OX16 7SP, United Kingdom. Manuscript submitted February 9, 1993.
METALLURGICAL TRANSACTIONS A
intergranularly and penetration of a tube wall can occur relatively fast. The intergranular attack is reported 13'41to be enhanced by the diffusion of silicon along grain boundaries from the cladding during the brazing cycle. This intergranular mode of attack is shown in Figure 1 for a conventional 3xxx alloy. To prevent this type of attack, various approaches have been tried, including sheet processing changes, lSl presumably to modify grain structure and deflect the corrosion path, or the production of an intermediate layer of a sacrificial alloy between the cladding and core 161 during hot roll bonding. The Alcan alloy, XH00, is an AI-Mn 3xxx alloy which uses the diffusion of silicon from the cladding to protect the core from corrosion attack and more importantly penetration of the tube wall. Interestingly, the approach of Wade and S c o t P ] is at odds with their subsequent explanation 171 for improved corrosion life in a 3xxx alloy for vacuum brazing. Scott et al. [7) indicate a similar corrosion protection to XH00 by sacrificial layer but give no details of alloy composition and little evidence to support mic
Data Loading...
