CONSTITUTIVE RELATIONSHIPS FOR THE HOT WORKING OF AA 3004 (A1-1.0Mn-1.2Mg)

摘要

Recrystallized plate of 3004 (0.96 percent Mn, 1.23 percent Mg, 0.37Fe) was subjected to hot torsion tests in the ranges 250 to 500 deg C and 0.1 to 10 s~(-1). The flow curves strain hardened to a broad peak and softened slightly towards a steady state regime. At higher temperature, T and lower strain rate d#epsilon#, the maximum stress #sigma# and the softening were lower and the fracture Strains were higher. The exponential law was found satisfactory, but the power law was not. The constants A, n, Q_(HW) for the equation: A(sinh #alpha##sigma#)~n= d#epsilon# exp (Q_(HW)/8.31 T) were derived for #alpha# ranging from 0.01 to 0.08 MPa~(-1). In the d#epsilon# dependence on #sigma#, n varies almost inversely with #alpha#, whereas in the Arrhenius plot, the slope varies almost linearly with #alpha#; Q_(HW) is almost constant for #alpha# in the range 0.03 to 0.08 MPa~(-1). The constants differed slightly for longitudinal and transverse specimens. The use of #alpha# =0.04 or 0.06 MPa~(-1) makes comparison with published data simpler; the agreements were reasonable given the variations in composition. In general, the behavior of 3004 is intermediate between 5005 and 5182. Optical microscopic examination revealed elongated grains in which the subgrains became more clearly defined as T rose and d#epsilon# diminished. Clearly dynamic recovery provided good hot workability through a reduced strain-energy, particle-stabilized substructure which also inhibited recrystallization unless the product was heated to about 50 deg above the deformation temperature as previously published.