Fractal analysis of the heat treatment response for multiphase Al alloys

Abstract

The present work shows the fractal analysis for the microstructure of Al-6Si-3Cu-xMg (x = 0.59, 3.80 and 6.78 wt.%) alloys, solution heat treated at 480 °C for times ranging from 4 to 72 h. Microstructural changes were examined using Optical Microscopy (OM) and Scanning Electron Microscopy (SEM), and quantified by measuring conventional characteristics of second phases. The fractal analysis of the microstructures was also carried out using fractal dimension (D f ). Results shown important variations in the microstructure when Mg content is increased, being the eutectic Al-Si and Cu-rich phases the predominant phases for the alloys with low Mg content, while for higher Mg contents predominant phases were Mg 2 Si and Cu-rich phases. The analysis of D f showed that this parameter could be used in order to compare the microstructural solution response of the Al alloys. Besides, it was possible to correlate the fractal dimension with the shape factor of the second phases, mainly for the alloys with only one second phase remaining after heat treatment.

Fractal and Conventional Analysis of Cu Content Effect on the Microstructure of Al-Si-Cu-Mg Alloys

“…Images modified using ImageJ are observed to the right side of SEM images, remarking Cu-rich phases (top) and Mg 2 Si (down). As a first overview, and according to literature and our previous works 1,3,5 , it can be observed that for the alloy with 3% Cu (Figure 1a) besides α-Al there are present two phases: i) Cu-rich phases (mainly light grey Q phase, and low quantity of white Al 2 Cu), and ii) Mg 2 Si (black), mainly eutectic. Few spaces free of second phases are observable (α-Al solid solution).…”

“…Research focused on aluminum alloys has been developed in an uninterrupted way in the last years, been published many works mainly related to microstructural modifications, which derivate from the presence of different second phases with a wide variety of morphologies, i.e. block-like, fibrillar, particulate, acicular, Chinese script, etc [1][2][3][4] . The presence of these phases in Al alloys directly depends on alloying elements content and manufacturing process, affecting their final mechanical properties.…”

“…The presence of these phases in Al alloys directly depends on alloying elements content and manufacturing process, affecting their final mechanical properties. Among these alloys is the quaternary Al-Si-Cu-Mg system, whose microstructure is composed by eutectic Si, Q (Al 5 Mg 8 Cu 2 Si 6 ), Al 2 Cu and Mg 2 Si, in addition to other complex intermetallic compounds 1,[5][6][7][8] . These alloys have Si contents between 5.5 and 6.5 wt.% and Cu from 3.0 to 4.0%.…”

“…A parameter previously used for characterizing complex phases is the fractal dimension (D f ), not only for Al alloys 1,18,19 but also for other materials with inclusions, as tourmalines in minerals 20 . D f is a measure of a geometry complexity: larger the dimension, the more heterogeneous and complex the fractal object is.…”

Modelling and Optimization for Heat Treatment of Al-Si-Mg Alloy Prepared by Indirect Squeeze Casting Based on Response Surface Methodology

“…If a relatively high temperature is applied the ageing time can be shortened. The time required to peak hardness is about 10h at 170ºC, while it is only 20minute at 210ºC 13,14 . However, a decrease in performance is discovered if the temperature is increased to 210ºC because the β″ phase change to the β′ phase when temperatures over 200ºC 15 .…”