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DESCRIPTION 6022 is a heat treatable low copper, Al-Si-Mg sheet alloy developed by Alcoa to satisfy the needs of automotive manufacturers for closure panels, such as a hood, decklid or a door. This alloy was developed to provide improved corrosion resistance, higher formability and greater strength for dent resistance after thermal exposure (paint bake) compared to other competitive offerings. It can satisfy the forming and strength requirements for both exterior body panel as well as structural applications. It can be provided as a coil or as blanks in tempers T4, T43 and T4E32. Alloy 6022 is being considered in many new body closurepanels programs by the global automotive community to take advantage of these superior performance attributes. Table 1: Chemical Composition Limits (wt. %) Alloying Element Alloy 6022 Alloy 6111 Alloy 6016 Si 0.8-1.5 0.6-1.1 1.0-1.5 Fe 0.05-0.20 0.40 0.50 Cu 0.01-0.11 0.50-0.9 0.20 Mn 0.02-0.10 0.10-0.45 0.20 Mg 0.45-0.70 0.50-1.0 0.25-0.6 Cr 0.10 0.10 0.10 Zn 0.25 0.15 0.20 Ti 0.15 0.10 0.15 Others, each 0.05 0.05 0.05 Others, total 0.15 0.15 0.15 Aluminum Remainder Remainder Remainder Note: Value is maximum, if range is not shown. APPLICATIONS With the appropriate design, alloy 6022 can provide weight savings on the order of 40-60%, compared to steel while matching its structural performance. It is not susceptible to Lüders or stretcher-strain lines, making it a good choice for surface quality critical applications. It is available in T4, T43 and T4E32 tempers which were developed to provide a balance of higher strength and formability with improved hemability. Temper-T43 may be used both for panels and reinforcements, whereas T4 temper is recommended primarily for reinforcements. The new variant, -T4E32, has been recently developed to further improve flat hemming performance and Class A painted surface quality of alloy 6022. Another significant advantage of 6022 is in the area of filiform corrosion resistance, where it performs better than alternative alloy choices. It provides strengths that are similar to more traditional alloys, but has forming characteristics that are better than or similar to those alloys. It can be artificially aged to increase yield strength for higher dent resistance of the formed part similar to or better than traditionally used alloys. Aluminum panels can be formed in the same number of steps as for steel and can be joined by a variety of methods. Finishing systems and repair methods are similar to those already in place for steel. MECHANICAL PROPERTIES 6022-T43, 6022-T4E32 and 6022-T4 sheet products offer relatively low strength and high elongations resulting in a very desirable combination of strength and formability for closure panel manufacturing. This favorable combination of mechanical properties is due to the optimized chemistry and processing employed by Alcoa in producing this family of products. As with most 6xxx series alloys, 6022 sheet experiences some amount of aging at ambient temperature following solution heat treatment. Mechanical properties after 30 days of natural aging are shown in the following table on page 2 (Table 2: Mechanical Properties of 6022-T43, 6022-T4E32 and 6022-T4 Sheet Products. Tested Per ASTM Method(s) B557.) 1 SPD-10-009
Table 2: Mechanical Properties of 6022-T43, 6022-T4E32 and 6022-T4 Sheet Products (Tested Per ASTM Method(s) B557) 6022-T43 (0.9 mm) 6022-T4E32 (1.0 mm) 6022-T4 (2.0 mm) Test Direction L 45 LT L 45 LT L 45 LT TYS (MPa) 137 131 129 135 129 127 142 137 133 UTS (MPa) 257 249 243 252 243 238 239 233 226 Elongation (%) 26 29 27 26 29 27 26 28 27 AFTER PAINT BAKE STRENGTH & RESPONSE Alloy 6022 provides greater strength and improved dent resistance after paint bake compared to other competitive alloys. Shown in the table below are the average mechanical properties following two simulated paint baking for two automotive sheet alloys. Table 3: Mechanical Property Comparison of two Automotive sheet Products 6022 T43 6016 T4 6022 T43 6016 T4P Mechanical 0.9mm gage 1.2mm gage 1.0mm gage 1.0mm gage Property* Paint bake at 170 C (338 F) Paint bake at 182 C (360 F) for 20 minutes for 32 minutes TYS (MPa) 227 143 272 239 UTS (MPa) 294 219 325 294 Elongation % 21 24 18 19 *Properties average of several samples in the long transverse direction tested per ASTM method(s) B557 after 2% pre-strain and paint bake thermal exposure The figures below show the change in tensile yield strength of 6022-T43 in response to varying times at various temperatures for two starting conditions of 0 and 2% pre-strain. Samples were tested in the orientation transverse to the rolling direction. As can be seen, the after paint bake strengths are higher with increasing levels of pre-strain. Also after paint bake response of 6022-T4E32 is very similar to the of 6022-T43. Figure 1: Tensile yield strength change of 6022-T43 sheet at various temperatures and times with (a) no pre-strain and (a) with 2% pre-strain. 2 SPD-10-009
The forming characteristic of 6022 T43 is very good. It displays superior performance in both laboratory evaluations and in field forming trials. Because of its enhanced forming characteristic, 6022 can often be utilized for both inner and outer panel automotive applications, thereby creating a uni-alloy (and potentially uni-gauge) assembly. Shown at right is the forming limit diagram for 0.9 mm thick 6022-T43 sheet. FORMABILITY Figure 2: Forming Limit Diagram of 6022-T43 Sheet (0.9 mm) HEMMING PERFORMANCE Hemming performance is one of the key requirements for closure panels. Customers increasingly prefer aluminum sheet product that is capable of flat hemming. Alcoa s 6022-T4E32 sheet is capable of flat hemming provided the pre-strains are not excessive in the area of the hem joint. As pre-strain levels increase, the quality of the hem decreases. The following photographs show typical flat hem test specimens using the newly developed 6022-T4E32 product. The sheet samples were pre-strained at 3 different levels prior to flat hemming. Specimens that were pre-strained to 7, 11 and 15% were rated at 1, 1 and 2, respectively, using the rating scale shown below. 15% pre-strain 11% pre-strain 7% pre-strain Rating 2 Rating 1 Rating 1 Hem Rating Scale 1 No cracking (mild to moderate orange peel is acceptable) 2 Heavy orange peel 3 Cracks visible with 3X magnification 4 Cracks visible with naked eye 5 Fracture or continuous crack along bend Hem Rating Acceptance Scale 1 & 2: Fully Acceptable 3: Marginal Subject to assembly plant decision 4 & 5: Not Acceptable Figure 3: Flat hem specimens of 6022-T4E32 sheet tested after pre-straining to different levels. 3 4/07
CORROSION RESISTANCE In various laboratory and outdoor tests, alloy 6022 has performed better than competing alloys in both the -T4 and -T43 after paint bake conditions. The tests that have been conducted include filiform corrosion of zinc-phosphated panels with various paint systems and intergranular corrosion of bare panels. Painted 6022 panels displayed shorter length and fewer sites of filiform corrosion than the traditional alloys. The extent and depth of intergranular corrosion was also less. Susceptibility to exfoliation and stress-corrosion cracking is expected to be minimal or non-existent for alloy 6022. With normal automotive paint procedures, in-service corrosion resistance is expected to be excellent. The following photograph (Figure 4) compares 6022 to 6111 and 6016 after 3 weeks of exposure to dry bottom MASTMAASIS per ASTM G85. Figure 4: Comparison of 6016-T4, 6022-T4 and 6111-T4 after 3 weeks of exposure to dry bottom MASTMAASIS per ASTM G85. Like all aluminum alloys in a corrosive environment, alloy 6022, when coupled with a dissimilar metal such as steel, is subject to galvanic corrosion. Proper protection must be provided to ensure that galvanic corrosion is minimized. For example, using galvanized steel and/or coating the steel will greatly reduce the galvanic attack. Additional protection can be provided through the use of sealants or adhesives. Thorough testing of the finished assembly is necessary to determine if the protection is adequate. (REF: SAE Paper 760166, Corrosion Performance of Painted Aluminum and Steel Body Sheet.) 4 SPD-10-009
JOINING Alloy 6022 may be mechanically clinched, adhesively bonded, welded or joined by self-piercing rivets. It can be resistance spot welded and arc welded in a manner similar to traditional alloy choices. When using arc welding, high silicon based filler alloys such as 4043, 4047 and 4145 are recommended. In order to achieve improved final weld strength, use of filler alloy 4145 with a post-weld thermal treatment is suggested. Also, in applications where the joint design provides limited filler metal dilution, such as a square butt joint, filler alloy 4145 is recommended. Resistance welding schedules, as well as other joining techniques are given in Tentative Guide to Automotive Resistance Spot Welding of Aluminum (Publication - T10, The Aluminum Association) and Welding Aluminum: Theory and Practice (The Aluminum Association.) FINISHING Outer-surface quality aluminum sheet provides a superior surface for automotive body panels. Alloy 6022 can be ordered with this surface quality specification and can be finished similar to other traditionally selected alloys. All of these alloys have been painted successfully in production paint systems designed for steel. In-plant handling and repair procedures are also similar to those for steel. For optimum repair of minor damage, specific files and sanding discs are recommended. REF: SAE Paper 740079, Finishing Considerations for Aluminum Body Sheet Alloys; and In-Plant Handling and Repair of Aluminum Auto Body Sheet (Publication - T16, The Aluminum Association.) SCRAP VALUE Because of the ability to utilize 6022 for both inner and outer body panels as well as structural reinforcements, there exists the potential for a single alloy scrap management program. This will enhance the value of that scrap, whether returned to Alcoa or sold directly to a scrap dealer. Typically, alloys in the 6xxx series have a slightly higher scrap value than 5xxx series alloys. REMARKS The 6022 alloy family offers an excellent combination of surface quality, after paint bake strength, formability and hemming performance. The composition of 6022 was designed to provide excellent filiform and inter-granular corrosion resistance. The properties described in this fact sheet are the best available current information. The end user is expected to evaluate and test the alloy, temper and finishing method for each specific application. Alcoa s warranty is limited to that published on the reverse side of its sales order acknowledgment form. 5 4/07