STRAIN RATE DEPENDENCE ON MECHANICAL PROPERTIES IN SOME COMMERCIAL ALUMINUM ALLOYS

Abstract

The flow stress and ductility of some commercial aluminum alloys (1050, 3003, 3004, 5182 and 7N01) have been investigated as a function of strain rates over the range from 1x10 s to 4xl0s at room temperature. The maximum flow stress of both 1050 and 3003 alloys increases with increasing strain rate , but the maximum flow stress of 3004, 5182 and 7N01 alloy decreases with increasing strain rate in the low and intermediate ranges from lx l 0 3 to lxl0 s 1 .The above three alloys which showed the particular behavior of flow stress in this strain rate range contain magnesium atoms in solute. So, this behavior of flow stress in these alloys seemed to be concerned with the interaction between magnesium atoms in solute and dislocations. The elongation in failure increases with strain rate for most of the present alloys except for the 7N01 alloy. 1-INTRODUCTION Recently many kinds of commercial aluminum alloys have been used in press forming, and the forming rates in use are in the strain rate range from 1 to 100 s 1 . Therefore, the investigation of the mechanical properties of commercial aluminum alloys in these forming rates is important to use these alloys appropriately. It is well known that the change of flow stress of aluminum[l] and aluminum alloys[2) with strain rate at room temperature is negligible in a low strain rate range below 10 s; but the flow stress increases rapidly with strain rate in high strain rate ranges over 10s. A few reports about mechanical properties for aluminum alloys, however, were made for the strain rate ranges from 10' s 1 to 10sM31. Therefore, the flow stress and ductility of some commercial aluminum alloys(1050, 3003, 3004, 5182 and 7N01) have been investigated as a function of strain rates over the range from lx lO 3 to 4xl0 s' at room temperature. Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jp4:1991349 C3-342 JOURNAL DE PHYSIQUE IV 2-EXPERIMENTAL PROCEDURE The chemical composition of the commercial aluminum alloys used in this study is given in Table 1. Tensile specimens, machined from hot rolled plates, had their tensile axes normal to the rolling direction. The gauge length of the specimen is 4.5 mm and the diameter is 3 rnm. All specimens were heated to 643 K with a heating rate of 47 K / hour and then annealed for 2 hours in air. The optical microstructures of these alloys after annealing are shown in Fig. 1 (a)-(e) respectively. The grains were elongated to the direction of rolling and fiber-structures are observed for all alloys. (a) 1050 alloy (b) 3003 alloy (c) 3004 alloy (dl 5182 alloy (e) 7N01 alloy Fig.1 The optical microstructures for all alloys after annealing Low strain rate tensile tests (lx103 l ~ l O ' s ~ ) were performed with an instron machine. and intermediate strain rate tensile tests (1x10-1-3x102s1) were performed with the hydraulic tensile testing machine, and the dynamic tensile tests (4x102 -4x103s-l) were performed using a split Hopkinson pressure bar system which incorporates a specific attachment. The incremental strain rate tests were performed by the hydraulic tensile testing machine. This machine has a valve corresponding proportionally to given voltage. Therefore, using a computer with a controlling voltage pattern, the constant strain rate tests or the incremental strain rate tests can be performed. Table 1 The chemical composition of the commercial aluminum alloys ELEMENT ( w t % ) ALLOY Z n Mg Cu Mn ~r Z r T i F e S i