B Rated Curled or easily broken chips and good to excellent surface finish

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1 7414 Alcoa 6020 Article 9/16/04 11:57 AM Page 1 Figure 1: Aluminum Alloy Machinability Ratings: Chip Size A Rated Very small broken chips and excellent surface finish B Rated Curled or easily broken chips and good to excellent surface finish C Rated Continuous chips and good surface finish Machining productivity is linked to alloy machinability. In lathe operations, a C rated performance is typically characterized by decreased tool feed rates and lower spindle speeds resulting in increased cycle times. The alloys also are susceptible to bird nesting, when continuous chips wrap themselves around the tooling, affecting part surface quality and requiring the machine to be turned off to clean the tooling. The chip trays on lathes also fill up faster with continuous chips and require the machine to be turned off for periodic cleaning more frequently than A rated alloys. All of these features negatively impact efficiency. In contrast, A rated machining performance is characterized by higher tool feed rates and higher spindle speeds lowering machined part cycle times. Chips are small and broken resulting in infrequent machine interruption for cleaning chip collection trays. UltrAlloy 6020 Development Parameters The development of 6020 was the result of a full factorial experimental design. Multiple compositional variants of copper (Cu), silicon (Si), magnesium (Mg) and tin (Sn) levels as well as the effects of tempering all were evaluated for machinability, mechanical properties and physical attributes. Sn was chosen to replace lead (Pb) for its ability to form low melting point eutectic phases in aluminum. These phases essentially provide internal chip breakers. Comparison of the chips produced during the machinability tests indicates that 6020 chips are comparable to Not only does 6020 demonstrate the very small broken chips of an A rated alloy, it also has an excellent surface finish. Processing of the alloy, from ingot casting through cold drawing and heat treatments, was investigated for optimal machined chip size due to impact of them on microstructure and ultimately the alloy s machinability. Metallographic tools, as well as differential scanning calorimetry and X-ray diffraction, were used to monitor alloy phase formation through processing as well as focus on improved machinability. Machinability testing was performed using CNC-type lathes with two standard machining tests. The ASTM E618 tool wear test was used to obtain the volume of chips produced in a certain number of machined parts, while single-point turning was employed to measure the number of chips per gram. Standard mechanical property testing was performed in accordance with ASTM B557. In addition, corrosion testing was performed in accordance with ASTM B117, GM4298P, ASTM G44, DOT 3 brake fluid exposure and ASTM G85 specifications. 2

2 7414 Alcoa 6020 Article 9/16/04 11:57 AM Page 2 Microstructure Typical free-machining alloys contain low melting point additives such as lead (Pb) and bismuth (Bi) to enhance the machining of the alloy and decrease machined chip size. In alloy 2011, the Pb and Bi alloy elements form a low melting eutectic compound of Pb3Bi + Bi with a eutectic point of 125 C. Alloy 6262 also contains Pb and Bi, but since 6262 also contains Mg, there is no low melting eutectic, but rather higher melting point compounds of Mg2Pb, melting at 248 C, and Mg3Bi2 with a melting point of 271 C. As a free-machining alloy, UltrAlloy 6020 contains chipbreaking constituents in its microstructure to aid in small chip formation during machining operations. These chip breaking constituents are primarily in the form of a low melting eutectic of ß-Sn+Mg2Sn whose eutectic temperature is 203 C. Since these eutectics have lower melting points than the Pb-Bi compounds found in 6262, the machining performance of both 2011 and UltrAlloy 6020 is superior to 6262 alloy. The low melting eutectics in UltrAlloy 6020 can be seen in the microstructure as shown in Figure 3. Figure 3: Microstructure of UltrAlloy 6020; 100X longitudinal, as polished Material Properties The material properties of UltrAlloy 6020 are shown in Table 3 along with commonly used machining aluminum alloys 2011, 2030, 6262, and Table 3: Typical Properties of Commonly Used Machining Aluminum Alloys Typical Properties Tensile Yield General Strength Strength Elong. Corrosion Anodize Alloy Temper (Mpa) (Mpa) % Resistance Machinability Brazing Welding Response 6020 T B A B B A T B A B B A 2030 T D A D D C T D A D C C T C A D C C T B B B B A T B B B B A 6061 T6/T B C A A A 4

3 7414 Alcoa 6020 Article 9/16/04 11:57 AM Page 3 Mechanical Strength Strength levels of UltrAlloy 6020 are similar to 2011 and 6262, as well as general purpose In the same tempers, UltrAlloy 6020 has a slightly lower tensile and yield strength when compared to Corrosion Resistance and Anodizing Response Corrosion testing performed by independent testing facilities found no visible corrosion after 72 hours exposure to DOT 3 brake fluid. Additionally, ASTM B117 5% salt spray solution exposure passed the 24-hour test requirement of GM-4298P. UltrAlloy 6020 showed no failures and no appreciable corrosion depth after ASTM G44 stress corrosion cracking exposure testing for 84 days. Additionally, no failures and corrosion attack were exhibited after ASTM B85 Mast-Maasis corrosion testing with 4 week exposure. The corrosion resistance behavior of UltrAlloy 6020 means excellent anodizing response, making alloy 6020 ideally suited for anodized applications including clear, clear and dyed, and hard coat anodizing. The above testing earned 6020 a B corrosion resistance rating and anodize response rating of A. Welding and Brazing UltrAlloy 6020 is slightly less brazeable than This is primarily due to the presence of low melting point Sn additions to enhance the machining performance. Brazing temperature controls between 582 C and 592 C are recommended and yield satisfactory brazing responses comparable to TIG, MIG and resistance welding methods also demonstrate acceptable welding results, earning UltrAlloy 6020 a B welding and brazing rating. The lower copper content of UltrAlloy 6020 provides improved brazing and welding ratings compared to free-machining 2xxx alloys. Applications UltrAlloy 6020 is ideally suited for precision machined parts is corrosion resistant and can be used for parts with anodize coatings, requiring traditional brazing and welding joining techniques. In today s increasingly competitive global business environment, this means that the increased productivity levels achieved by using 6020 mean better bottom line financial results for parts manufacturers due to lower manufacturing costs. Common applications for 6020 and their associated productivity improvements are shown in Table 4. Table 4: Typical Applications of UltrAlloy 6020 and Productivity Improvement Evaluation Candidates Application Cycle Time Decrease using T T8 A/C Fitting 50% 6262-T T8 Master Cylinder Brake Piston 22% 6262-T T9 A/C Charge Valve 20% 6061-T T8 Recreational Products (Fishing Reel, 30% Rifle Scope, flashlight casing) 6262-T T8 Transmission Valves 10% Common applications for 6020 are heavily machined parts where chip management issues require improved machinability. These include recreational products such as rifle scopes, flashlight casings and fishing reels where 6020 has meant an average 30% decrease in machine part cycle times. Automotive components such as transmission valves, spools and sleeves, air conditioning charge ports and fittings have been produced with 6020, resulting in a 10-50% decrease in machined part cycle times. These successes have led to investigating 6020 for other automotive applications such as fittings. 5

4 7414 Alcoa 6020 Article 9/16/04 11:57 AM Page 4 UltrAlloy 6020 Test Results Testing resulted in Alcoa UltrAlloy 6020 whose composition is shown in Table 1. UltrAlloy 6020 is available in the T8 and T9 tempers for improved machinability over other lead-free aluminum alloys and improved machinability over the most commonly used lead-containing alloys 2011 and Mechanical strength levels, chemical response to anodizing, corrosion resistance and the welding/brazing response of 6020 are comparable to 6262 and 6061 alloys. Machinability Alcoa s UltrAlloy 6020 helps machined parts producers not only meet the needs to use alloys without lead alloying additives, but it also improves machining productivity and increases machine shop competitiveness. The composition and thermal-mechanical processing of 6020 UltrAlloy produce an average of 250 chips/gram with a typical surface finish of 41 RMS as shown in Table 2 and Figure 2. Chip sizes of UltrAlloy 6020 were found to be slightly smaller than 2011 and were much smaller than those of Table 1: Chemical Composition of Common Machining Aluminum Alloys Si Fe Cu Mn Mg Cr Ti Sn Pb Bi OE.OT / / / / /0.15 Element values listed in weight percent maximum unless a range is listed. OE/OT represents Other Each and Others Total. Others includes listed elements for which no specific limit is shown as well as unlisted metallic elements. Table 2: Typical Machined Chip Size and Surface Finish of Machining Aluminum Alloys Alloy Typical Chip Size (#chips/gram) Typical Surface Roughness (RMS) Overall Rating UltrAlloy A A B Note: Machined surface roughness measured on profilometer after single point turning surface; RMS represents root mean square calculated as times the arithmetic mean measured roughness. Figure 2: Photographs of Chips from Machining Aluminum Alloys Note: 4000 RPM, 1046 SFM using 15 degree rake angle with chip-breaker

5 7414 Alcoa 6020 Article 9/16/04 11:57 AM Page 5 UltrAlloy 6020 not only provides improved productivity in machining, it can also add value by eliminating certain secondary or off-line operations. Highly machined parts from 2011, for example, will typically require an anodize coating to increase corrosion resistance in applications where additional corrosion protection is needed. Due to UltrAlloy 6020 chemistry and processing, the alloy shows superior corrosion resistance compared to 2011 and often times the added corrosion protection may not be required for Eliminating the off line anodizing process saves the parts producer the extra cost and time associated with anodizing finished machined parts. This can also provide value to finished parts, since coatings can often be undermined due to scratching or wear in use. Summary The environmental impacts of products are driving many changes in the materials science and materials applications. The days of pending legislation have passed and it s time for manufacturers to think about environmental impacts of products and processes up front. Alcoa s UltrAlloy 6020 does just that it s lead free, has earned an A rating for machinability and ultimately benefits not only the environment, but also the bottom line of parts manufacturers. UltrAlloy 6020: Contains no purposeful lead additions Is rated A for machining performance Offers machinists higher productivity than machining other 6xxx alloys, particularly 6061 and even 6262 Displays the traditional beneficial 6xxx alloy characteristics in terms of corrosion resistance, anodizing, brazing and welding. Shows superior corrosion resistance and anodize response to 2011 and other 2xxx alloys. Has strength levels similar to other aluminum screw machine stock alloys Acknowledgements The authors would like to thank Tom Klemp, Debbie Sienkiewycz, and Lori Gallagher for their review and preparation of this paper. References 1. Environmental Protection Agency, Internet Website. 2. Handbook of Aluminum: Volume 1 Physical Metallurgy and Processes, Editors, G. E. Totten and D. S. MacKenzie. pg U. S. Patent, #5,522,950, granted International Alloy Designations and Chemical Composition Limits for Wrought Aluminum and Aluminum Alloys, Aluminum Association, October UltrAlloy 6020: A Lead-Free Aluminum Alloy Featuring "A" Rated Machinability, Colleen M. Spillard, SAE International Congress and Exposition, February 23-26, 1998, Document #

6 7414 Alcoa 6020 Article 9/16/04 11:57 AM Page 6 Alcoa s UltrAlloy 6020: A Lead-Free Aluminum Alloy With A-Rated Machinability Ideally Suited for Precision Machined Parts Brian J. Edwards Gerald D. Scott Alcoa Abstract Over the past two decades there has been a significant movement to eliminate lead and lead-containing products in the U.S. and abroad. For example, Since the 1980s, the U.S. Environmental Protection Agency (EPA) and its federal partners have phased out lead in gasoline, reduced lead in drinking water, reduced lead in industrial air pollution and banned or limited lead used in consumer products, including residential paint. Like the EPA, the European Union is also looking to greatly reduce lead contamination in the environment, most notably with recent RoHS and ELV directives. Within the metals industry, lead removal has been a dilemma for the majority of parts manufacturers. Could they successfully convert from existing lead-containing feed stocks to lead-free stocks without a sacrifice in productivity and performance in end uses and applications? Traditional lead-free aluminum alloys commonly used have not been able to demonstrate small chip formation, necessary to enhance shop productivity, common in free machining lead-containing alloys until now. All of that changed with the introduction of Alcoa s UltrAlloy 6020 alloy. Alcoa removed the lead as an alloying element and developed an alloy that has an A rating for machinability. UltrAlloy 6020 is a 6XXX alloy with all of the inherent six series advantages: corrosion resistance, joinability, anodizability, etc. that provides machined chips comparable to 2011 commonly recognized as the benchmark for aluminum alloy machinability. Alcoa s UltrAlloy 6020 helps machined-parts producers not only remove lead from aluminum precision machined parts, but it also increases machining productivity and machine shop competitiveness. Machinability of Aluminum Alloys Alloy 2011 has been a staple in machined aluminum parts for decades because of the small chips that it generates during machining. European analogues to 2011 are alloys 2007 and This is significant, because small chips typically mean higher productivity and reduced cycle times therefore saving parts manufacturers valuable time and money. Machinability is typically rated by chip size and resultant machined surface finish. Alloy ratings are either A, B, C, D and E in increasing order of chip length and decreasing order of quality of finish. A rated or free cutting alloys have chips that are very small and broken with excellent machined surface finish. Alloys 2011, 2007 and 2030 provide this type of machining performance. B rated machinability chips are curled or easily broken with good to excellent machined surface finish. Alloy 6262 is a B rated machining alloy. C rated alloys have continuous chips with a satisfactory machined surface finish. Alloy 6061 is a C rated machining alloy. See Figure 1 for photographic depictions of typical chip size ratings. 1