TABLE OF CONTENTS Wrought alloys that respond to strengthening by heat treatment are covered by the three series 2xxx (Al Cu, Al Cu Mg), 6xxx (Al Mg Si) and 7xxx (Al Zn Mg, Al Zn Mg Cu). All depend on age-hardening to develop enhanced strength properties and they can be classified into two groups: those that have medium strength and are readily weldable (Al Mg Si and Al Zn Mg), and the high-strength alloys that have been developed primarily for aircraft construction (Al Cu, Al Cu Mg, and Al Zn Mg Cu), most of which have very limited weldability. Compositions of representative commercial alloys are shown in Table 3.4, and Table 3.5 gives typical properties, the forms in which they are available, together with some common applications.
Although the complex changes that occur during the ageing of Al Cu alloys have been studied in greater detail than any other system, there are actually few commercial alloys based on the binary system. Alloy 2011 (Al 5.5Cu) is used where good machining characteristics are required, for which it contains small amounts of the insoluble elements lead and bismuth that form discrete particles in the microstructure and assist with chip formation. Alloy 2025 is used for some forgings although it has largely been superseded by 2219 (Al 6.3Cu) which has a more useful combination of properties and is also available as sheet, plate and extrusions. Alloy 2219 has relatively high tensile properties at room temperature together with good creep strength at elevated temperatures and high toughness at cryogenic temperatures. In addition, it can be welded and has been used for...
