Strengthening mechanisms in solid solution aluminum alloys
- PDF / 260,606 Bytes
- 8 Pages / 612 x 792 pts (letter) Page_size
- 13 Downloads / 247 Views
NTRODUCTION
NON–HEAT-TREATABLE aluminum alloys constitute a class of alloys that owe their strength mainly to elements in solid solution and the grain size, and in some cases also to particles. Heat treatment of such an alloy will generally not produce any strengthening precipitates as in the heattreatable alloys. The strength may in fact decrease during heat treatment due to the removal of solute atoms (an exception is the precipitation of dispersoids in Al-Mn alloys). The alloy systems belonging to this class are the AA1xxx system (commercially pure with small amounts of mainly Fe and Si), the AA3xxx system (with manganese addition), and the AA5xxx system (with magnesium addition). Non–heat-treatable alloys are used in a wide range of applications where a low to medium strength, a good formability, and a good corrosion resistance are desirable. Beverage cans and automotive panels are two examples out of many. The introduction of foreign atoms into a crystal lattice invariably increases the strength of the material. A huge amount of work was done on the solid solution hardening in the 1950s and 1960s. Dorn et al. performed a systematic piece of work where they explored the effects of several alloying elements on the properties of binary aluminium alloys.[1,2] A classic paper on solution hardening is the one by Fleischer and Hibbard,[3] while a more recent review is given by Haasen.[4] The solid solution hardening is a result of an interaction between the mobile dislocations and the solute atoms. A number of mechanisms have been suggested.[4,5] However, the most relevant mechanisms for substitutional alloying of aluminium are the elastic interactions due to (1) the size ØYVIND RYEN and BJØRN HOLMEDAL, Postdoctoral Students, OSCAR NIJS, Diploma Student, and ERIK NES, Professor, are with the Department of Materials Science and Engineering, Norwegian University of Science and Technology, Trondheim, Norway. Contact e-mail: erik.nes@ ¨ LANDER, Diploma Student, is with the material.ntnu.no EMMA SJO Department of Physics, Royal Institute of Technology, Stockholm, Sweden. ¨ M, Manager, is with Sapa Technology, Finspong, HANS-ERIK EKSTRO Sweden. Manuscript submitted August 12, 2005. METALLURGICAL AND MATERIALS TRANSACTIONS A
misfit, where the size of the solute atom differs from the size of the matrix atoms and creates a strain field around the atom, and (2) the modulus misfit, where the difference in binding force between the solute atoms and the matrix atoms results in a hard or soft ‘‘spot’’ in the matrix. However the interaction works, the presence of solute atoms increases the initial yield stress and reduces the dynamic recovery rate of dislocations. This results in a higher dislocation density and a higher work hardening rate but also a different dislocation structure, which is dealt with in another paper.[6] Several authors have reported correlations between the flow stress and the alloy concentration of the type: s 5 spure 1 Hcn
[1]
where spure is the flow stress of a pure metal and H and n are constants. There seems
Data Loading...
