2.138 Chapter 2 Mechanical gouging can be done with rotary cutter machines de- signed for this purpose. Routers developed from woodworking tools are also used to shape aluminum. Aluminum can also be chemically milled, usually with sodium hydroxide based or other alkaline solu- tions. A typical removal rate is 0.0001 in. (0.0025 mm) per minute. Metal removal is controlled by masking, duration of immersion, and composition of the bath. 2.8 Joining 2.8.1 Welding Welding is the process of uniting parts by either heating, applying pressure, or both. Welding is like the little girl who, when she was good, was very, very good and, when she was bad, was horrid. Im- proper welding can be awful, while correctly designed and executed welds can solve problems intractable by other means. When heat is used to weld aluminum (as is usually the case), it reduces the strength of all tempers other than annealed material, and this must be taken into account where strength is a consideration. Also, welding alumi- num is different from welding steel, and most steel welding tech- niques are not transferable to aluminum. Aluminum’s affinity for oxygen, which quickly forms a thin, hard oxide surface film, has much to do with the welding process. This ox- ide is nearly as hard as diamonds, attested to by the fact that alumi- num oxide grit is often used for grinding. It has a much higher melting point than aluminum itself [3725°F (2050°C), versus 1220°F (660°C)], so trying to weld aluminum without first removing the oxide melts the base metal long before the oxide. The oxide is also chemi- cally stable; fluxes to remove it require corrosive substances that can damage the base metal unless they are fully removed after welding. Finally, the oxide is an electrical insulator and porous enough to re- tain moisture. For all these reasons, the base metal must be carefully cleaned and wire brushed immediately before welding, and the weld- ing process must remove and prevent reformation of the oxide film during welding. The metal in the vicinity of a weld can be considered as two zones: the weld bead itself, a casting composed of a mixture of the filler and the base metal, and the heat affected zone (HAZ) in the base metal outside the weld bead. The extent of the HAZ is a function of the thick- ness and geometry of the joint, the welding process, the welding proce- dure, and preheat and interpass temperatures, but it rarely exceeds 1 in. (25 mm) from the centerline of the weld. The strength of the metal near a weld is graphed in Figure 2.7. Smaller welds and higher 02Kissell Page 138 Wednesday, May 23, 2001 9:52 AM Aluminum and Its Alloys 2.139 welding speeds tend to have a smaller HAZ. As the base metal and filler metal cool after freezing, if the joint is restrained from contract- ing and its strength at the elevated temperature is insufficient, hot cracking may occur. The magnitude of the strength reduction from welding varies: for non-heat-treatable alloys, welding reduces the strength to that of the annealed (O) temper of the alloy; for heat-treatable alloys, the reduced strength is slightly greater than that of the solution heat treated but not artificially aged temper (T4) of the alloy. Minimum tensile strengths across groove welded aluminum alloys are given in Table 2.39. These strengths are the same as those required to qualify a welder or weld procedure in accordance with the American Welding Society (AWS) D1.2 Structural Welding Code—Aluminum and the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code, Section IX. They are based on the most common type of welding (gas-shielded arc, discussed next) and, as long as a recommended filler alloy is used, they are independent of filler. Yield strengths for welded material are also given in the Aluminum Association’s Aluminum Design Manual, but they must be multiplied by 0.75 to obtain the yield strength of the weld-affected metal, because the Association’s yield strengths are based on a 10 in. (250 mm) long gage length, and only about 2 in. (50 mm) of that length is heat affected metal. Fillet weld shear strengths are a function of the filler used; mini- mum shear strengths for the popular filler alloys are given in Figure 2.7 Strength near a weld. 02Kissell Page 139 Wednesday, May 23, 2001 9:52 AM 2.140 Chapter 2 TABLE 2.39 Minimum Strengths of Welded Aluminum Alloys Alloy Product Thickness (in.) Tensile ultimate strength (ksi) Tensile yield strength (ksi) 1060 sheet and plate up thru 3.000 8 2.5 1060 extrusion all 8.5 2.5 1100 all up thru 3.000 11 3.5 2219 all all 35 – 3003 all up thru 3.000 14 5 Alclad 3003 tube all 13 4.5 Alclad 3003 sheet and plate up to 0.500 13 4.5 Alclad 3003 plate 0.500 to 3.000 14 5 3004 all up thru 3.000 22 8.5 Alclad 3004 sheet and plate up to 0.500 21 8 Alclad 3004 plate 0.500 to 3.000 22 8.5 5005 all up thru 3.000 15 5 5050 all up thru 3.000 18 6 5052 all up thru 3.000 25 9.5 5083 forging all 39 16 5083 extrusion all 39 16 5083 sheet and plate up thru 1.500 40 18 5083 plate > 1.500, thru 3.000 39 17 5083 plate > 3.000, thru 5.000 38 16 5083 plate > 5.000, thru 7.000 37 15 5083 plate > 7.000, thru 8.000 36 14 5086 all up thru 2.000 35 14 5086 extrusion > 2.000, thru 5.000 35 14 5086 plate > 2.000, thru 3.000 34 14 5154 all up thru 3.000 30 11 5254 all up thru 3.000 30 11 02Kissell Page 140 Wednesday, May 23, 2001 9:52 AM Aluminum and Its Alloys 2.141 Table 2.40. Fillet welds transverse (perpendicular) to the direction of force are generally stronger than fillet welds longitudinal (parallel) to the direction of force. This is because transverse welds are in a state of combined shear and tension, and longitudinal welds are in shear, and tension strength is greater than shear strength. Heat-treatable base metal alloys welded with heat-treatable fillers can be heat treated after welding to recover strength lost by heat of welding. This post-weld heat treatment can be a solution heat treat- ment and aging or just aging (see Section 2.2.3). While solution heat treating and aging will recover more strength than aging alone, the 5454 all up thru 3.000 31 12 5456 extrusion up thru 5.000 41 19 5456 sheet and plate up thru 1.500 42 19 5456 plate > 1.500, thru 3.000 41 18 5456 plate > 3.000, thru 5.000 40 17 5456 plate > 5.000, thru 7.000 39 16 5456 plate > 7.000, thru 8.000 38 15 5652 all up thru 3.000 25 9.5 6005 extrusion up thru 1.000 24 – 6061 all all 24 – Alclad 6061 all all 24 – 6063 extrusion up thru 1.000 17 – 6351 extrusion up thru 1.000 24 – 7005 extrusion up thru 1.000 40 – 356.0 casting all 23 – 443.0 casting all 17 7 A444.0 casting all 17 – 514.0 casting all 22 9 535.0 casting all 35 18 TABLE 2.39 Minimum Strengths of Welded Aluminum Alloys (Continued) Alloy Product Thickness (in.) Tensile ultimate strength (ksi) Tensile yield strength (ksi) 02Kissell Page 141 Wednesday, May 23, 2001 9:52 AM 2.142 Chapter 2 rapid quenching required in solution heat treating can cause distor- tion of the weldment because of the residual stresses that are intro- duced. Natural aging will also recover some of the strength; the period of time required is a function of the alloy. The fillet weld strengths for 4043 and 4643 in Table 2.40 are based on 2 to 3 months of natural aging. Prior to 1983, the ASME Boiler and Pressure Vessel Code, Section IX, Welding and Brazing Qualifications was the only widely available standard for aluminum welding. Many aluminum structures other than pressure vessels were welded in accordance with the provisions of the Boiler and Pressure Vessel Code, therefore, due to the lack of an alternative standard. In 1983, the American Welding Society’s (AWS) D1.2 Structural Welding Code—Aluminum was introduced as a gen- eral standard for welding any type of aluminum structure (e.g., light poles, space frames, etc.). In addition to rules for qualifying aluminum welders and weld procedures, D1.2 includes design, fabrication, and inspection requirements. There are other standards that address spe- cific types of welded aluminum structures, such as ASME B96.1 Welded Aluminum-Alloy Storage Tanks, AWS D15.1 Railroad Welding Specification—Cars and Locomotives, and AWS D3.7 Guide for Alumi- num Hull Welding. 2.8.1.1 Gas-shielded arc welding. Before World War II, shielded metal arc welding (SMAW) using a flux coated electrode was one of the few ways aluminum could be welded. This process, however, was ineffi- cient and often produced poor welds. In the 1940s, inert gas-shielded TABLE 2.40 Minimum Shear Strengths of Filler Alloys Filler alloy Longitudinal shear strength (ksi) Transverse shear strength (ksi) 1100 7.5 7.5 2319 16 16 4043 11.5 15 4643 13.5 20 5183 18.5 – 5356 17 26 5554 17 23 5556 20 30 5654 12 – 02Kissell Page 142 Wednesday, May 23, 2001 9:52 AM Aluminum and Its Alloys 2.143 arc welding processes were developed that used argon and helium in- stead of flux to remove the oxide, and they quickly became more popu- lar. Other methods of welding aluminum are used (and will be discussed below), but today most aluminum welding is by the gas- shielded arc processes. There are two gas-shielded arc methods: gas metal arc welding (GMAW), also called metal inert gas welding or MIG, and gas tung- sten metal arc welding (GTAW), also called tungsten inert gas welding or TIG. MIG welding uses an electric arc between the base metal be- ing welded and an electrode filler wire. The electrode wire is pulled from a spool by a wire-feed mechanism and delivered to the arc through a gun. In TIG welding, the base metal and, if used, the filler metal are melted by an arc between the base metal and a nonconsum- able tungsten electrode in a holder. Tungsten is used because it has the highest melting point of any metal [6170°F (3410°C)] and reason- ably good conductivity—about one-third that of copper. In each case, the inert gas removes the oxide from the aluminum surface and pro- tects the molten metal from oxidation, allowing coalescence of the base and filler metals. TIG welding was developed before MIG welding and was originally used for all metal thicknesses. Today, however, TIG is usually limited to material 1/4 in. (6 mm) thick or less. TIG welding is slower and does not penetrate as well as MIG welding. In MIG welding, the electrode wire speed is controlled by the welding machine and, once adjusted to a particular welding procedure, does not require readjustment, so even manual MIG welding is considered to be semiautomatic. MIG welding is suitable for all aluminum material thicknesses. The weldability of wrought alloys depends primarily on the alloying elements, discussed below for the various alloy series: 1xxx: Pure aluminum has a narrower melting range than alloyed aluminum. This can cause a lack of fusion when welding, but gener- ally the 1xxx alloys are very weldable. The strength of pure alumi- num is low, and welding decreases the strength effect of any strain hardening, so welded applications of the 1xxx series are used mostly for their corrosion resistance. 2xxx: The 2xxx alloys are usually considered poor for arc welding, being sensitive to hot cracking, and their use in the aircraft typically has not required welding. However, alloy 2219 is readily weldable, and 2014 is welded in certain applications. 3xxx: The 3xxx alloys are readily weldable but have low strength and so are not used in structural applications unless their corrosion resistance is needed. 02Kissell Page 143 Wednesday, May 23, 2001 9:52 AM 2.144 Chapter 2 5xxx: The 5xxx alloys retain high strengths, even when welded, are free from hot cracking, and are very popular in welded plate struc- tures such as ship hulls and storage vessels. 6xxx: The 6xxx alloys can be prone to hot cracking if improperly de- signed and lose a significant amount of strength due to the heat of welding, but they are successfully welded in many applications. Postweld heat treatments can be applied to increase the strength of 6xxx weldments. The 6xxx series alloys (like 6061 and 6063) are of- ten extruded and combined with the sheet and plate products of the 5xxx series in weldments. 7xxx: The low-copper-content alloys (such as 7004, 7005, and 7039) of this series are weldable; the others are not, losing considerable strength and suffering hot cracking when welded. Some cast alloys are readily welded, and some are postweld heat- treated, because they are usually small enough to be easily placed in a furnace. The condition of the cast surface is key to the weldability of castings; grinding and machining are often needed to remove contami- nants prior to welding. The weldability of the 355.0, 356.0, 357.0, 443.0, and A444.0 alloys is considered excellent. Filler alloys can be selected based on different criteria, including re- sistance to hot cracking, strength, ductility, corrosion resistance, ele- vated temperature performance, MIG electrode wire feedability, and color match for anodizing. Recommended selections are given in Table 2.41, and a discussion of some fillers is given below. Material specifica- tions for these fillers are given in AWS A5.10, Specification for Bare Aluminum and Aluminum Alloy Welding Electrodes and Rods. There is no ASTM specification for aluminum weld filler. Filler alloys 5356, 5183, and 5556 were developed to weld the 5xxx series alloys, but they have also become useful for welding 6xxx and 7xxx alloys. Alloy 5356 is the most commonly used filler due to its good strength, compatibility with many base metals, and good MIG elec- trode wire feedability. Alloy 5356 also is used to weld 6xxx series al- loys, because it provides a better color match with the base metal than 4043 when anodized. Alloy 5183 has slightly higher strength than 5356, and 5556 higher still. Because these alloys contain more than 3% magnesium and are not heat treatable, however, they are not suit- able for elevated temperature service or postweld heat treating. Alloy 5554 was developed to weld alloy 5454, which contains less than 3% magnesium so as to be suitable for service over 150°F (66°C). Alloy 5654 was developed as a high-purity, corrosion-resistant alloy for welding 5652, 5154, and 5254 components used for hydrogen per- oxide service. Its magnesium content exceeds 3%, so it is not used at elevated temperatures. 02Kissell Page 144 Wednesday, May 23, 2001 9:52 AM Aluminum and Its Alloys 2.145 Alloy 4043 was developed for welding the heat-treatable alloys, es- pecially those of the 6xxx series. Its has a lower melting point than the 5xxx fillers and so flows better and is less sensitive to cracking. Alloy 4643 is for welding 6xxx base metal parts over 0.375 in. (10 mm) to 0.5 in. (13 mm) thick that will be heat treated after welding. Alloys 4047 and 4145 have low melting points and were developed for braz- ing but are also used for some welds; 4145 is used for welding 2xxx al- loys, and 4047 is used instead of 4043 in some instances to minimize hot cracking and increase fillet weld strengths. Alloy 2319 is used for welding 2219; it’s heat treatable and has higher strength and ductility than 4043 when used to weld 2xxx alloys that are postweld heat treated. Pure aluminum alloy fillers are often needed in electrical or chemi- cal industry applications for conductivity or corrosion resistance. Alloy 1100 is usually satisfactory, but for even better corrosion resistance (due to its lower copper level), 1188 may be used. These alloys are soft and sometimes have difficulty feeding through MIG conduit. The filler alloys used to weld castings are castings themselves (C355.0, A356.0, 357.0, and A357.0), usually 1/4 in. (6 mm) rod used for TIG welding. They are mainly used to repair casting defects. More recently, wrought versions of C355.0 (4009), A356.0 (4010), and A357.0 (4011) have been produced so that they can be produced as MIG elec- trode wire. (Alloy 4011 is only available as rod for GTAW, however, since its beryllium content produces fumes too dangerous for MIG welding.) Like 4643, 4010 can be used for postweld heat treated 6xxx weldments. Weld quality may be determined by several methods. Visual inspec- tion detects incorrect weld sizes and shapes (such as excessive concav- ity of fillet welds), inadequate penetration on butt welds made from one side, undercutting, overlapping, and surface cracks in the weld or base metal. Dye penetrant inspection uses a penetrating dye and a color developer and is useful in detecting defects with access to the surface. Radiography (making X-ray pictures of the weld) can detect defects as small as 2% of the thickness of the weldment, including po- rosity, internal cracks, lack of fusion, inadequate penetration, and in- clusions. Ultrasonic inspection uses high-frequency sound waves to detect similar flaws, but it is expensive and requires trained personnel to interpret the results. Its advantage over radiography is that it is better suited to detecting thin planar defects parallel to the X-ray beam. Destructive tests, such as bend tests, fracture (or nick break) tests, and tensile tests are usually reserved for qualifying a welder or a weld procedure. Acceptance criteria for the various methods of in- spection and tests are given in AWS D1.2 and other standards for spe- cific welded aluminum components or structures. 02Kissell Page 145 Wednesday, May 23, 2001 9:52 AM 2.146 02Kissell Page 146 Wednesday, May 23, 2001 9:52 AM 2.147 02Kissell Page 147 Wednesday, May 23, 2001 9:52 AM [...]... Fluid in entire brazing range 40 45 BA1Si–5 10 – – 1070–1095 (577–591) 1090–1120 (588–6 04) X X X 40 04 BA1Si–7 10 – 1.5 1030–11052 1090–1120 (5 54 596)2 (588–6 04) X X Vacuum furnace brazing 41 47 BA1Si–9 12 – 2.5 1 044 –10802 1080–1120 (562–582)2 (582–6 04) X X Vacuum furnace brazing 41 043 BA1Si–11 10 – 1.5 1030–11052 1090–1120 (5 54 596)2 (588–6 04) X X Vacuum furnace brazing 40 44 ––– 8.5 – 1070–11152 1100–1135... 15 1090–1120 (588–6 04) No 21 1 No 24 2 No 33 1 No 34 0.090 and less 2.29 and less 10 1100–1150 2.3 and over 5 (593–621) 0.090 and less 2.29 and less 10 1090–1120 2.3 and over 5 (588–6 04) All All 10 1100–1135 2 No 44 see note 43 43 10 7.5 0.091 and over 2 No 23 6951 0.62 to 1.59 1.60 and over 0.091 and over 1 No 22 0.025 to 0.062 0.063 and over 6951 40 45 6951 40 44 (593–613) 1 6951 40 44/ 7072 All All 15/5... available in 20 24- T4, 6061-T6, and 6262-T9 with properties conforming with ASTM F467, Nonferrous Nuts for General Use Full thickness nuts of 6262-T9 are strong enough to develop the full strength of bolts made of 20 24- T4, 6061-T6, or 7075-T73; nuts of 6061-T6 are strong enough to develop the full strength of 20 24- T4 and 6061-T6 bolts Machine screw nuts and other styles of small nuts [1 /4 in (6 mm) and... 23, 2001 9:52 AM 2.160 Chapter 2 TABLE 2 .47 Rivet Specifications Alloy and temper Specification number Grade or code 1100-F MIL-R-56 74 A 2017-T4 MIL-R-56 74 D 2117-T4 MIL-R-56 74 AD 20 24- T4 MIL-R-56 74 DD 5056-H32 MIL-R-56 74 B 6053-T61 MIL-R-1150 E 6061-T6 MIL-R-1150 F 1100-F AMS 7220 99A1 20 24- T4 AMS 7223 4. 5 Cu, 1.5 Mg, 0.6 Mn 2117-T4 AMS 7222 2.5 Cu, 0.3 Mg 2017-T4 FF-R-556 B Other Fasteners Aluminum nails... Diffuse bright Other C40 C41 Organic solvent treated Inhibited chemical type cleaner used To be specified Trisodium phosphate, 22 45 g/l (3–6 oz per gal) used at 60–71°C ( 140 –160°F) for 3 to 5 min Sodium hydroxide, 30 45 g/l (4 6 oz per gal) used at 49 –66°C (120–150°F) for 5 to 10 min Sodium fluoride, 11g/l (1.5oz) plus sodium hydroxide 30 45 g/l (4 6 oz per gal) used at 54 66°C (130–150°F) for 5 to 10 min... amount by which the diameter of hole is enlarged should be at least 1 /4 of the thickness of the piece and no less than 1/32 in (0.8 mm) Punching should be limited to material that is no thicker than the diameter of the hole to avoid tear out at the back side of the work For design purposes such as the determination of the net cross-sectional area of the part at a hole, the size of punched holes is taken... 0. 24 mm (0.0095 in.); peripheral wheel speed 30 m/s (6,000 ft/min.); or various proprietary satin finishing wheels or satin finishing compounds with buffs To be specified 02Kissell Page 1 64 Wednesday, May 23, 2001 9:52 AM TABLE 2 .48 2.1 64 Mechanical Finishes (M) Type of finish Designation1 Unspecified Extra fine matte Fine matte M43 Medium matte M 44 Coarse matte M45 Fine shot blast M46 Medium shot blast M47... Number of sides cladding Core alloy Cladding composition Sheet in No 7 1 3003 40 04 No 8 2 No 11 1 No 12 2 No 13 1 No 14 2 6951 40 04 0.0 24 and less 0.61 and less 15 1090–1120 0.62 to 1.59 1.60 and over 10 7.5 (588–6 04) 0.063 and less 1.60 and less 10 1100–1150 0.0 64 and over 43 43 Brazing range °F (°C) 0.025 to 0.062 0.063 and over 3003 mm % Cladding on each side 1.62 and over 5 (593–621) 0.0 24 and less... in (6 mm) and smaller] are usually made of 20 24- T4 Flat washers are usually made of alclad 20 24- T4 and helical spring washers of 7075-T73 Galvanized and plated steel and austenitic stainless steel bolts are also used to fasten aluminum parts Galvanized, high-strength (ASTM A325) steel bolts can be used in joints that are designed to prevent slip of the connected parts relative to each other, because... shear strength (ksi) 1100-H 14 9.5 2017-T4 33 2117-T4 26 5056-H32 25 6053-T61 20 6061-T6 25 7050-T7 39 Screws Wood and sheet metal screws are made of 20 24- T4 or 7075-T73 aluminum; austenitic stainless steel screws may also be used to connect aluminum parts Equations for the shear and tensile strengths of tapping screw connections in aluminum parts can be found in the Specification for Aluminum Structures, . less 10 1090–1120 No. 24 2 0.091 and over 2.3 and over 5 (588–6 04) No. 33 1 6951 40 44 All All 10 1100–1135 No. 34 2 (593–613) No. 44 see note 1 1 This product is Clad with 40 44 on one side and 7072. the 545 4 all up thru 3.000 31 12 545 6 extrusion up thru 5.000 41 19 545 6 sheet and plate up thru 1.500 42 19 545 6 plate > 1.500, thru 3.000 41 18 545 6 plate > 3.000, thru 5.000 40 17 545 6. low melting points and were developed for braz- ing but are also used for some welds; 41 45 is used for welding 2xxx al- loys, and 40 47 is used instead of 40 43 in some instances to minimize hot