HEAT-TREATABLE ALLOYS
The heat-treatable alloys attain maximum strength through controlled heat treatment either before or after forming operations. They are the highest strength alloys—hard, with good appearance, and generally good resistance to corrosion and abrasion. They are particularly suited for structural applications and other uses requiring both formability and strength, and highly stressed end products.
ALLOY 2011
Machining: Offers the best machinability and is therefore widely used for commercial screw machine parts. Free machining compares favorably with free cutting brass and frequently replaces free machining brass without necessitating a conversion in tooling. This is the most suitable alloy for machining on automatics, milling machines, lathes, planers and other machine tools. Because of the very small broken chips, can be machined at high speeds with comparatively heavy feeds. Because of the free machining characteristics of 2011, tool wear with this alloy is less than with the other standard screw machine alloys.
Finishing may be accomplished by all the standard finishes, both mechanical and chemical, which may be applied to any other aluminum alloy. Machined surfaces are bright and smooth and readily match joined parts. Anodizing for any length of time produces a yellow cast attributable to the alloying constituents of the alloy.
Welding: This alloy is not recommended for welding or brazing.
Typical End Uses: Screw machine products, wiring devices and fittings, brake pistons, optical parts, electrical components, ball point pens, radio and TV components.
ALLOY 2024, BARE AND ALCLAD
Corrosion Resistance in the heat-treated condition is only fair. Of course, corrosion resistance is enhanced greatly by cladding and where corrosive environments are to be encountered 2024 should not be used without cladding protection.
Finishing can be carried out by any of the processes applicable to aluminum alloys; however, the anodizing of this material will not provide a color match nearly as consistent as other alloys. A pleasing finish may be applied to 2024 by the use of a clear conversion coating over either mill finish or polished surface. The clear conversion coating is then covered with a clear lacquer coat Under these circumstances the color match between 2024 and any other alloy finished by the same system is excellent
Welding by resistance methods is feasible. Fusion welding though not normally recommended can be done with proper procedures and equipment What has been said about heat and corrosion resistance should be remembered, however, and applied to the fusion welding problem. When welded, 2024 is hot short (brittle); consequently, fixtures or joints should be designed to minimize strain of the weld zone during the cooling period. Brazing and soldering are not recommended.
Machining is relatively good in either 0, T4 or T351 tempers, with the latter temper producing best results. The major machining problem is the production of a long stringy chip; hence, drills and taps should have highly polished flutes to assist chip flow. Because it has high strength. Alloy 2024 is recommended for parts and for structures requiring a good strength-weight ratio.
Workability of 2024 in the annealed condition is good. Also immediately following solution heat treating the alloy is readily formed; however, after four hours of natural aging there is difficulty experienced with any but the simplest forming. In fact, severe forming should be done from Vs to 1 hour following solution heat treating. This alloy is susceptible to much deformation as a result of the rapid temperature change which takes place upon quenching from the solution heat treating temperature; hence, any form which would be too difficult to straighten
should be formed immediately following heat treating. Hot working of 2024 is not recommended unless the material is subsequently heat-treated since a considerable loss in corrosion resistance may result.
Thermal Operations (anneal cycle, 0 temper): To remove the effects of cold work use a metal temperature of 650°F. Time at temperature is unimportant. The time in the furnace need not exceed that necessary to bring the entire load up to annealing temperature. To remove the effect of heat treatment, use a metal temperature of 775 °F The time in the furnace after the entire load has been brought up to annealing temperature should be 2-3 hours. When annealing to remove the effects of heat treatment a cooling rate of 50°F per hour down to
500°F should be used. The subsequent cooling rate need not be controlled.
ALLOY 6061
Corrosion Resistance is good, in fact this alloy resists atmospheric and chemical corrosion better frian any other commercially produced heat-treatable sheet or plate product. Further, the corrosion resistance of 6061 is, for all practical purposes, independent of the temper and for many uses the material does not require any paint or other means of protection.
Finishing may be done by any of the standard finishing practices normally applied to aluminum. The material takes an excellent anodic finish provided care has been exercised in the removal of the heat treat stains. Paint finishes are best applied after the removal of such stains also.
Welding is readily accomplished by any of the processes normally used to weld aluminum alloys. Welding does not lower the corrosion resistance of the alloy but there is some loss of mechanical properties in the weld area and heat affected zone, when welding the heat-treated tempers. Resistance welding may be carried out by the flash, seam and spot welding methods. Inert gas, both with the tungsten and consumable electrodes, is preferred for fusion welding applications. Brazing and soldering by all methods are feasible, but trial runs may be necessary to establish the best methods.
Machining of this alloy produces good results; the rating is excellent compared to other aluminum sheet and plate alloys. Machining of 6061, like machining of most other aluminum alloys, requires the use of toots which are sharp and well polished and which are run at high speeds with copious amounts of lubricant cascading over the tools and work surface. A strong tough alloy, 6061 is the most versatile of the heat-treatable alloys. Alloy 6061 is often referred to as a magnesium-silicide alloy, that is, it contains magnesium and silicon in the ratio of two parts magnesium to one part silicon which form the magnesium-silicide compound.
Magnesium-silicide alloys are lower in strength than copper alloys, such as 2024, but this is offset by a much greater degree of workability especially in the T4 temper.
Workability in the "0" condition is quite similar to 5005 and 5050 in the same condition but in the heat treated (T4) state and in the heat treated and aged condition (T6) the workability is much like that of 5052 in the H34 and H38 condition. Considerable forming and bending may be done in theT6 condition. However, it is generally recommended that all drawing be attempted in the T4 or 0 conditions. Parts which can be successfully formed or drawn in the T4 temper may be given an aging, precipitation, treatment to raise their properties to the full T6
strength level.
Thermal Operations (anneal cycle, 0 temper): To remove the effects of cold work, use a metal temperature of 650°F. Time at temperature is unimportant The time in the furnace need not exceed that necessary to bring the entire load up to annealing temperature. To remove the effects of heat treatment use a metal temperature of 775 °F. The time in the furnace after the entire load has been brought up to annealing temperature should be 2-3 hours. When annealing to remove the effects of heat treatment a cooling rate of 50°F per hour down to 500°F should be used. The subsequent cooling rate need not be controlled.
Typical End Uses: Aircraft landing mats, aircraft water storage tanks, architectural
sections, billboard sign panels.
ALLOY 6063
Corrosion Resistance is excellent in rural, industrial and marine exposures.
Finishing: As-extruded finish is bright with a minimum of die lines and pickup, often highly satisfactory without further work. Anodizing to a clear color, and electrochemical, organic, and mechanical finishes may be applied after proper preparation.
Weldability is excellent by all commonly used methods, except that resistance weldability is not satisfactory in the 0 temper.
Machinability is considered fair especially in the harder tempers. Tungsten carbide tipped tools can be advantageous for long production runs where tool wear is a problem. Tools should be kept sharp and well polished.
Typical End Uses: 6063 is the leading architectural extrusion alloy for windows, doors, curtain wall components, building hardware, etc. It is widely used for furniture tubing, ladder parts, conduit irrigation tubing, marine applications, moldings, handrails, etc.
ALLOY 6101
Corrosion resistance is excellent in rural, industrial and marine environments. Chemical and organic coatings also give excellent results where extra protection is required.
Finishing frequently requires silver plating ends of bus bars, in which case surface should be relatively free of die lines, imperfections, lubricants and other contaminants.
Weldability is excellent by all usual methods.
Machinability is considered generally comparable to that of 6063, especially in the harder tempers.
Typical End Uses: Alloy 6101 was developed specifically for electrical bus conductor applications with conductivities of 55-60 I.A.C.S. It is a magnesium-silicide, precipitation-hardening alloy for moderate strength applications.
ALLOY 6262
Newest of standard screw-machine stock alloys, this was developed to combine ease of machining with high corrosion resistance. Machinability in T9 temper equals that of 2011-T3 and is superior to all other SSMS alloys. It may replace 2017, 2024 and 6061 in most machining applications. Formability is fair in T6 temper, difficult in T9. Bright smooth machine finish is easy to obtain.
:
ALLOY 7075, BARE AND ALCLAD
Corrosion Resistance, when heat treated and fully aged, is fair. The corrosion resistance of magnesium silicide alloys like 6061 is much better. For increased corrosion protection, Alloy 7075 is also supplied with a cladding of Alloy 7072 which has a nominal 1 zinc content The resultant product is quite satisfactory as evidenced by the use of Alclad 7075-T6 sheet for aircraft.
Finishing: Anodic coatings are applied for corrosion protection only.
Weldability by the fusion method gives inferior results and is not recommended. Resistance welding, spot and seam may be readily accomplished with clad material in the T6 condition. Resistance welding of the bare material is not recommended due to the severe loss in corrosion resistance which occurs as a result of such welding attempts. Brazing and soldering are not recommended.
Machining requires high surface speed of the cutter to accomplish good results. Cutter speeds are in the range of 700 to 3000 feet per minute. Machine setups should be rigid and cuts should be steady with depths of cut being approximately 20 less for full hard material than for annealed material. In general, tools should be sharp, of the positive rake type and possess a good amount of clearance.
One of the Highest Strength Alloys commercially available, 7075 is basically a zinc alloy. It exhibits a high degree of notch sensitivity and care must be taken not to create stress risers such as nicks and deep scratches during the working of sheet or plate into its final form. In working this material in the solution heat treated condition, it strain hardens more rapidly than 2024, but age hardens more slowly at room temperature. There is little or no warping of 7075 in the age hardening treatment of parts which have been formed in the heat treated condition.
Workability is extremely low in the T6 temper, It is best formed immediately after quenching. In the 0 condition, 7075 can be successfully formed on all types of equipment but because of its higher yield strength, a greater allowance will have to be made for springback than for most other aluminum alloys. The use of heat up to 250°F during forming in the annealed state may be of considerable help in certain swaging, spinning and drop hammer operations. Since annealing is a rather elaborate process, severe forming in the 0 condition is not very practical.
By refrigerating at 0 degrees F the formability of the material in the "W" condition may be maintained for approximately two weeks.
Thermal Operations (anneal cycle, 0 temper): To remove the effect of cold work and/or heat treatment, use a metal temperature of 775 °F. The time in the furnace after the entire load has been brought up to annealing temperature should be 2-3 hours. A cooling rate of 100°F down to 450°F should be used. When the load has cooled to 450°F it should be held at that temperature for 4 hours. This alloy can also be air cooled, but if the metal is to be stored for an extended length of time before use, the anneal should be followed by heating to 450°F and holding for 6 hours.
ALLOY 7178
Corrosion Resistance is only fair for many applications, calling for protection such as organic or anodized coatings, or alclad form, for severe environments.
Finishing by electrochemical, chemical, or organic finishes combines corrosion resistance with attractive appearance. Machined surfaces can be bright and smooth, and standard mechanical finishes are effective.
Weldability considered good for resistance methods. Arc welding can be effective, but care must be taken to insure against intergranular melting resulting in embrittlement Gas welding and brazing are not recommended.
Machinability is good. especially in the harder tempers, in which depth of cut should be approximately 20 less than for annealed material. As with other aluminum alloys, high surface speeds, high positive rakes and clearances, rigid setups, and plenty of coolant-lubricant five optimum results.
Forming is more difficult in the cold state than with most alloys, but its strength is so high that it is selected for many specialized applications. Stress risers such as small nicks and deep scratches should be avoided, especially during final working operations.
Strength is highest among commercially available alloys.
Typical Thermal Treatments: Annealing to remove effects of solution heat treatment requires 2 to 3 hours at 775 °F, followed by furnace cooling at uncontrolled rate to 400°F or less, followed by reheating to 450°F for 4 hours. Removal of effects of cold work. or partial removal of effects of heat treatment may be accomplished by treatment at 650°F followed by uncontrolled cooling.