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INTRODUCTIONHigh-strength aluminum alloys used as a structural material in supersonic passenger aircrati must have a satisfactory level of crack resistance characteristics such as fracture toughness and resistance to fatigue fracture in addition to the requisite combination of strength properties at room and elevated temperatures and stability in heating and service [I].Despite the numerous tests of commercial high-temperature alloys and their relatively recent modifications, the literature gives very scarce data on comparative analysis of their properties obtained for identical semiproducts with close types of structure [2,3].The aim of the present work was to obtain a set of characteristics of static strength and crack resistance in similar semiproducts produced from the most widely used domestic high-temperature defon'nable aluminum alloys in order to compare them and rank them in accordance with individual parameters. METHODS OF STUDYWe studied commercial special-purpose high-temperature alloys D21, VDI7, and D19ch [2] and new high-temperature aluminum alloys 1215 and AK4-2ch, which are modifications of alloys D21 and AK4-1ch, respectively [4,5]. Alloy AK4-1ch has not been studied in the present work because AK4-2ch is much more preferable [4]. The alloys (Table 1 ) were cast by a semicontinuous method into flat ingots with a cross section of 90 • 220 mm and into ingots 134 mm in diameter, taking each alloy from one heat. After hornogenizing and mechanical treatment the ingots were used to fabricate rolled and pressed semiproducts. We pressed strips with a cross section of 10 • 100 mm at 450~ from turned ingots 124 mm in diameter. Flat ingots with a cross section t All-Russia Institute of Light Alloys, Moscow, Russia. 266 of 80 • 190 mm were hot rolled at 400~ without cladding to a thickness of 6 ram. Then they were annealed and cold rolled to a thickness of 2 mm with a degree of delormation equal to 67%.The pressed strips and rolled sheets were simultaneously quenched in water after a 40-rain hold in a vertical quenching furnace at 500~ for semiproducts from alloys VD17 and Dl9ch and at 525~ for semiproducts fu alloys D21, 1215, and AK4-2ch. The semiproducts were dressed by stretching with a residual detbrmation of I -2% in a lYeshly quenched state. In all cases the pressed strips had a fiber nonrecrystallized structure in their central volumes and a coarse-crystalline border about 1 mm thick over the periphery. In fabricating the specirnens this border was cut off. The rolled sheets had a fine-grained recrystallized structure. All the preforms for making specimens were aged simultaneously at 190~ for6h (alloys D21 and 1215) and for 16 h (alloys VD17, AK4-2ch, and D I 9ch), which provided a state TI in the alloys with strength characteristics close to the maximum on the aging curve.For the pressed strips we determined the mechanical properties in tensile tests at room and elevated temperatures using longitudinal rupture specimens with the diarneter of the functional part equal to 5 mm and the design length e...