Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C21/00—Alloys based on aluminium
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C21/00—Alloys based on aluminium
  • C22C21/10—Alloys based on aluminium with zinc as the next major constituent

Definitions

• the invention relates to a high corrosion resistant aluminium alloy, especially an alloy intended to be used for manufacture of automotive air conditioning tubes for applications as heat exchanger tubing or refrigerant carrying tube lines, or generally fluid carrying tube lines.
• the alloy has extensively improved resistance to pitting corrosion and enhanced mechanical properties especially in bending and endforming.
• aiuminium alloy materials for automotive heat exchange components are now widespread, applications including both engine cooling and air conditioning systems.
• the aluminium components include the condenser, the evapora- tor and the refrigerant routing lines or fluid carrying lines. In service these components may be subjected to conditions that include mechanical loading, vibration, stone impingement and road chemicals (e.g.. salt water environments during winter driving conditions).
• Aluminium alloys of the AA3000 series type have found extensive use for these applications due to their combination of relatively high strength, light weight, corrosion resistance and extrudability. To meet rising consumer expectations for durability, car producers have targeted a ten-year service life for engine coolant and air conditioning heat exchanger systems.
• the AA3000 series alloys (like AA3102, AA3003 and AA3103), however, suffers from extensive pitting corrosion when subjected to corrosive environments, leading to failure of the automotive component. To be able to meet the rising targets/requirements for longer life on the automo- tive systems new alloys have been developed with significantly better corrosion resistance. Especially for condenser tubing, 'long life' alloy alternatives have recently been developed, such as those disclosed in US-A-5,286,316 and WO-A-97/46726. The alloys disclosed in these publications are generally alternatives to the standard AA3102 or AA1100 alloys used in condenser tubes, i.e. extruded tube material of relatively low mechanical strength.
• the corrosion focus have shifted towards the next area to fail, the manifold and the refrigerant carrying tube lines.
• the fluid carrying tube lines are usually fabricated by means of extrusion and final precision drawing in several steps to the final dimension, and the dominating alloys for this application are AA3003 and AA3103 with a higher strength and stiffness compared to the AA3102 alloy.
• the new requirements have therefore created a demand for an aluminium alloy with processing flexibility and mechanical strength similar or better than the AA3003/AA3103 alloys, but with improved corrosion resistance.
• the object of this invention is to provide an extrudable, drawable and brazeable aluminium alloy that has improved corrosion resistance and is suitable for use in thin wall, fluid carrying tube lines. It is a further object of the present invention to provide an aluminium alloy suitable for use in heat exchanger tubing or extrusions. It is another object of the present invention to provide an aluminium alloy suitable for use as finstock for heat exchangers or in foil packaging applications, subjected to corrosion, for instance salt water. A still further object of the present invention is to provide an aluminium alloy with improved formability during bending and end-forming operations.
• an aluminium-based alloy consisting of 0,05 - 0,15 % by weight of silicon, 0,06 - 0,35 % by weight of iron, 0,01 - 1 ,00 % by weight of manganese, 0,02 - 0,60 % by weight of magnesium, 0,05 - 0,70 % by weight of zinc, 0 - 0,25 % by weight of chromium, 0 - 0,20 % by weight of zirconium, 0 - 0,25 % by weight of titanium, 0 - 0,10 % by weight of copper, up to 0,15 % by weight of other impurities, each not greater then 0,Q3 % by weight and the balance aluminium.
• the manganese content is between 0,50-0,70 % by weight, more preferably 0,62 - 0,70 % by weight.
• the addition of manganese contributes to the strength, however, it is a major point to reduce the negative effect manganese have with respect to precipitation of manganese bearing phases during final annealing, which contributes to a coarser final grain size.
• Addition of magnesium results in a refinement of the final grain size (due to storage of more energy for recrystallization during deformation) as well as improvements the strain hardening capacity of the material. In total this means improved formability during for instance bending and endforming of tubes.
• Magnesium also has a positive influence on the corrosion properties by altering the oxide layer.
• the content of magnesium is preferably below 0,3 % by weight due to its strong effect in increasing extrudability. Additions above 0,3 % by weight are generally incompatible with good brazeabiiity.
• the level of this element should be kept low to make the alloy more recycleable and save cost in the cast house. Otherwise, zinc has a strong positive effect on the corrosion resistance up to at least 0,70 % by weight, but for the reasons given above the amount of zinc is preferably between 0,10 - 0,30 % by weight, more preferably 0,20 - 0,25 % by weight.
• the iron content of the alloy according to the invention is between 0.06-0.22 % by weight.
• a low iron content preferably 0,06 - 0,18 % in weight, is desirable for improved corrosion resistance, as it reduces the amount of iron rich particles which generally creates sites for pitting corrosion attack. Going too iow in iron, however, could be difficult from a casthouse standpoint of view, and also, has a negative influence on the final grain size (due to less iron rich particles acting as nucleation sites for recrystallization). To counterbalance the negative effect of a relatively low iron content in the alloy other elements has to be added for grainstructure refinement.
• another preferred iron content for many practical applications is 0,18 - 0,22 % by weight, giving a combination of excellent corrosion properties, final grain size and casthouse capability.
• the silicon content is between 0,05-0,12 % by weight, more preferably between 0,06 - 0,10 % by weight. It is important to keep the silicon content within these limits in order to control and optimise the size distribution of AIFeSi-type particles (both primary and secondary particles), and thereby controlling the grain size in the final product.
• chromium in the alloy For recycleability some chromium in the alloy is desirable. Addition of chromium, however, increases the extrudability and influences negatively on the tube drawability and therefore the level is preferably 0,05-0,15 % in weight.
• the zirconium content is preferably between 0,02-0,20 % in weight, more preferably between 0,10-0,18% in weight. In this range the extrudability of the alloy is practically not influenced by any change in the amount of zirconium
• the copper content of the alloy should be kept as low as possible, preferably below 0.01 % by weight, due to the strong negative effect on corrosion resistance and also due to the negative effect on extrudability even for small additions.
• Table 1 The alloys have been prepared in a traditional way by DC casting of extrusion ingots. Note that the composition of the alloys have been indicated in % by weight, taking into account that each of these alloys may contain up to 0.03 % by weight of incidental impurities. Compositions were selected with varying amounts of the different major elements. Note that alloy 1 in Table 1 is the composition of the standard AA3103 alloy, which is used as reference alloy in the investigation.
• Table 1 Chemical composition of alloys (% by weight).
• composition of the billets were determined by means of electron spectroscopy.
• a Baird Vacuum Instrument was used, and the test standards as supplied by Pechi- ney, were used.
• Extrusion billets were homogenised according to standard routines, using a heating rate of 100°C/hr to a holding temperature of approximately 600°C, followed by air cooling to room temperature.
• the extrudability is related to the die pressure and the maximum extrusion pressure (peak pressure). Those parameters are registered by pressure transducers mounted on the press, giving a direct read out of these values.
• the extruded base tube were finally plug drawn in totally six draws to a final 9.5 mm OD tube with a 0.4 mm wall. The reduction in each draw was approximately 36 %. After the final draw the tubes were soft annealed in a batch furnace at temperature 420°C.
• Corrosion potential measurements were performed according to a modified version of the ASTM G69 standard test, using a Gamry PC4/300 equipment with a saturated calomel electrode (SCE) as a reference.
• the tube specimens were degreased in acetone prior to measurements. No filing or abrasion of the tube specimen surface was performed, and the measurements were done without any form of agitation. Corrosion potentials were recorded continuously over a 60 minute period and the values presented represents the average of those recorded during the final 30 minutes of the test.
• the corrosion resistance was tested using the so-called SWAAT test (Acidified Synthetic Sea Water Testing).
• SWAAT test Acidified Synthetic Sea Water Testing
• the test was performed according to ASTM G85-85 Annex A3, with alternating 30 minutes spray periods and 90 minutes soak periods at 98 % humidity.
• the electrolyte used was artificial sea water acidified with acetic acid to a pH of 2.8 to 3.0 and a composition according to ASTM standard D1141.
• the temperature in the chamber was kept at 49°C.
• the test was run in a Erichsen Salt Spray Chamber (Model 606/1000).
• Table 2 summarises the results of the draw ability test. Table 2.
• n-value means strain hardening exponent, obtained by fitting a Ludwik law expression to the true stress-strain curve in the region between yield and uniform strain. ** grain size measured along the drawing direction on longitudinal tube cross sections. *** alloy is tested in H14 temper condition.
• test alloys generally have a more negative potential (more anodic) as compared to the reference alloy 1.
• Adding zinc, zirconium and/or titanium strongly drags the potentials to more negative values.
• the fact that these Long Life alloys have a more negative potential is important information with respect to corrosion design criteria, i.e. the importance of selecting appropriate material combinations in application were the tube is connected to a fin/header material (for instance in a condenser), is emphasised. In order for the tube not to behave sacrificial towards the fin/header, materials being more anodic than the Long Life tube needs to be selected.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Extrusion Of Metal (AREA)
• Prevention Of Electric Corrosion (AREA)
• Rigid Pipes And Flexible Pipes (AREA)
• Powder Metallurgy (AREA)
• Secondary Cells (AREA)
• Dowels (AREA)
• Extrusion Moulding Of Plastics Or The Like (AREA)
• Cookers (AREA)
• Laminated Bodies (AREA)
• Conductive Materials (AREA)
• Catalysts (AREA)

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• 1999
  • 1999-04-13 US US09/291,255 patent/US20020007881A1/en not_active Abandoned
• 2000
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