Heat-treatable aluminum alloys

It should be noted that a number of aluminum alloys are available (see Table 28-16). Many have improved mechanical properties over pure aluminum. The wrought heat-treatable aluminum alloys have tensile strengths of 90 to 228 MPa (13,000 to 33,000 Ibf/in ) as annealed when they are fuUy hardened, strengths can go as high as 572 MPa (83,000 Ibf/in"). However, aluminum alloys usually have lower corrosion resistance than the pure metal. The alclad alloys have been developed to overcome this snortcoming. Alclad consists of an aluminum layer metaUurgicaUy bonded to a core alloy. 

Table 3.31. Effect of Heat Treatment on Heat-Treatable Aluminum Alloys...

Effect of heat treatment on heat-treatable aluminum alloys. 89... 

G139, Standard Test Method for Determining Stress Corrosion Resistance of Heat-Treatable Aluminum Alloy Products using Breaking Load Method, ASTM, West Conshohoken, PA, 1996. 

Non-Heat-Treatable Alloys. Non-heat-treatable aluminum alloys are defined primarily by what they are not. They are not strengthened by second-phase particles and may be better described as non-precipitation-hardening alloys. The non-heat-treatable alloy classes are the Ixxx, 3xxx, and 5xxx alloys. 

Chapter 4, Microstructure Development in Aluminum Alloy Friction Stir Welds, discusses the main microstructural observations in the FSW of wrought aluminum alloys. The evolution of microstructure in welded heat treatable aluminum alloys has been modeled in great detail. The methods were mostly developed for arc welding and have been more recently applied to the thermal cycles inFSW (Ref4,72-79). For the heat-affected zone, the problem is purely thermal for the TM AZ and nugget, there is the potential added complexity of coupling between the deformation microstructure and precipitation. 

Alloy 7039 is essentially a ternary alloy of Al-4%Zn-3%Mg without the appreciable amounts of copper common to the older commercially available aluminum alloys of the 7000 series. Its composition, as registered with the Aluminum Association, is shown in Table I. It has a density of 0.0988 lb/in.3, an electrical conductivity at 68 °F of 35 % I ACS, and a modulus of elasticity at 75°F of 10 x 10 psi. It is heat-treatable, weldable, and has good general and stress corrosion resistance. It can be rolled into sheet or plate and can be extruded or forged. Its formability in the annealed temper is superior to most other heat-treatable aluminum alloys. It is currently undergoing ASTM registration in the -T61 temper. 

ASTM Standard G 110, Standard Practice for Evaluating Intergranular Corrosion Resistance of Heat Treatable Aluminum Alloys by Immersion in Sodium Chloride + H2O2 Solutions, Annual Book of ASTM, 1999, 03.02. 

GllO-92, Standard practice for evaluating intergranular corrosion resistance of heat treatable aluminum alloys by immersion in sodium chloride + hydrogen peroxide solution. Annual Book of ASTM Standards, ASTM International, Philadelphia, Pa., 2000, p. 481, Vol. 3.02. 

Testing of Intergranular Attack This necessitates metallographic examination (30). The Standard Practice ASTM GUO (1992) involves evaluation of IGC resistance of heat-treatable aluminum alloys by immersion in a sodium chloride and... 

Susceptibility to intergranular corrosion dep>ends primarily on the typ>e of alloy and fabrication process and can occur in most environments. The six-hour ASTM G 110 test (Practice for Evaluating Intergranular Corrosion Resistance of Heat Treatable Aluminum Alloys by Immersion in Sodium Chloride + Hydrogen Peroxide Solution) is most often used to determine inherent susceptibility to this form of corrosion. However, users are cautioned that the degree of susceptibility in this accelerated test may not be representative of p>erformance in outdoor atmospheres [22]. 

Classification of Resistance to Stress-Corrosion Cracking of Heat-Treatable Aluminum Alloys. 

Barrier coatings are of two types. The first consists of a thin surface layer of a more resistant metal. This can be accomplished by roll bonding (e.g.. stainless steel to non-heat-treatable aluminum alloys), by chrome plating, or by vapor deposit or ion deposition of a variety of metals. The latter methods are expensive and have size limitations. Unlike Alclad coatings, metal barrier coatings do not provide any electrochemical protection at a break in the coating. 

Intergranular anodic test for heat-treatable aluminum alloys 505... 

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