Mathematical modeling and optimization of precipitation hardening of extrudable aluminium alloys.

Abstract

Al-Mg-Si alloys (6xxx series alloys) are very popular in extrusion industry and are generally known as high speed erxtrusion alloys. Extrusion die solution treatment and press quenching greatly facilitates the precipitation hardening process since only the last aging process needs to be done. Time temperature choice is quite critical to get an optimum result. Strength and time plots for certain values of temperatures are available in literature, which are quite valuable if decisions are made manually. However, if selection is to be made automated or we need the strength response at temperature not available in these plots, we need appropriate mathematical model for interpolating the results. A research is therefore conducted and the objective of the study is to develop suitable mathematical models which correlate strength (yield strength and tensile strength) and process parameters (aging time and aging temperature) for each family of aluminium alloys. Aging characteristic curves of yield and tensile strength of three popular alloys of the family namely AA6061, AA6063, and AA6069 are analyzed. Based on the nature of these curves, a generalized mathematical model is developed for each alloys. Stepwise results are tabulated and comprehensive comparison of predicted curves and actual curves is presented. Based on the model, cost optimization of the aging process is discussed in a general framework. The objective of the optimization study is to explore an approach to get a target strength with a minimum possible cost. Both aging parameters (time and temperature) are used simultaneously to get the minimum cost zones respectively.