تجزیه و تحلیل حساسیت طریق فرآیند بر اثر متغیرهای فرآیند در قدرت در اکسترود آل گرم سی

A concept of through-process modelling for studying the effect of process variables on the strength of extruded Al–Mg–Si alloys is presented. Five models are integrated to model casting, homogenisation, extrusion and ageing of the alloys. It is demonstrated that through-process modelling can be utilised to study isolated effects from variations in processing parameters along the value chain on the strength in the end product, which is usually difficult to obtain from experiments. In the present work it has been focused on strength after artificial ageing and the most critical parameters to follow were therefore the Mg and Si and whether these elements appear in solid solution or present in constituent phases. The as-cast and homogenised structures were predicted reasonably well by the models, and it was found that the casting parameters have a significant influence on the density of constituent particles. Chemical composition and cooling rate from extrusion temperature are the variables with the most prominent effect on the yield stress of extruded and aged sections.

Consistent control of mechanical properties is crucial for all kinds of extruded aluminium products, including sections for the building industry, profiles for structural applications in the automotive industry and tubes for the heat transfer segment. Extruded aluminium sections are generally sold with a specific strength required by the customer, which varies quite significantly depending on the application. Usually, the claim from customers is a minimum strength-limit, which is met by the producers by aiming for strength well above this limit to account for the strength variations caused by the production processes. Recently, customers have started to require a maximum strength-limit in addition to the minimum limit. The required strength-limit-window can often be quite narrow, and it has therefore become crucial for extruders to be able to reduce the strength variability in the extruded sections. Reducing variations from production processes is not a simple task, and the complexity increases with increasing numbers of process steps and process parameters. A reasonable approach to the task is to identify the process parameters with the most significant impact on the variability, and make actions on these. One way to identify these parameters is to do a sensitivity analysis on measured data obtained from production. However, the available data might not cover every parameter, making it insufficient for pinpointing the governing factors. Implementing new parameters into the production database is generally expensive, as is dedicated experiments in the plant. Computer modelling and simulation offer an alternative to real life data, and is a cheaper and less time consuming way to solve the task. The objective of the present paper is to show the potential of applying through-process modelling as a tool for analysing the sensitivity of various process parameters on the final strength in extruded Al–Mg–Si alloys (AA6xxx series alloys), which is used in the majority of extruded aluminium sections. The task of modelling the strength of extruded AA6xxx sections is basically to keep track of the Mg and Si in solid solution through the process stages, and to predict the amount of the strength-enhancing β″-Mg5Si6 phase, described by Andersen et al. (1998), precipitated during the final age hardening stage. This is accomplished by combining existing available models, developed for each process stage, into a through-process modelling scheme. This scheme is used in a sensitivity analysis on the effect of process parameters on the yield stress of extruded and aged sections. Similar through-process modelling approaches have recently been reported by Engler et al. (2007) and Furu et al. (2004). These approaches combined microchemistry models, appropriate microstructure models for deformation and recrystallisation and finite element models (FEMs). The latter were used to provide the thermomechanical history along the process chain, from casting to semi-finished product, which served as input for the microchemistry and microstructure models. In this way they were able to describe the microstructure and texture evolution during a number of process steps from casting to semi-finished products, e.g. rolled sheet and extruded profiles. The present work makes use of similar types of models, however, it is focused mainly on the microchemistry changes themselves and the final strength after ageing, while those former works focused on microstructure and texture and their relations to properties.