Nazia Nafsin - BUET Central Library

0411112026P, session April 2011, has been accepted as satisfactory for partial fulfillment of the requirements for the degree of Master of Science in Materials and Metallurgical Engineering in June 2013. Hossain Mohammad Mamun Al Rashed, Assistant Professor, Department of Materials and Metallurgical Engineering (MME) , Bangladesh University of Engineering and Technology (BUET) for his continuous guidance, help, suggestions and encouragement during the progress of the project work. The author expresses her sincere gratitude to the Head of Department of MME, Professor Dr.

The author expresses her most heartfelt thanks to all the teachers and employees of the Department of Education and Training, who directly or indirectly help her during this work. 97 4.55 Effect of heat treatment on the hardness of Al-Cu alloy with 0%Mg 97 4.56 Effect of heat treatment on the hardness of Al-Mg alloy with 6%Cu 98 4.57 Formation of Mg-containing phases with increasing Mg content.

LIST OF TABLES

LIST OF ABBREVIATIONS

ABSTRACT

INTRODUCTION

For this development, research into the effects of different alloying elements on the microstructure is necessary. Phases can be predicted for both equilibrium and non-equilibrium Scheil-Gulliver solidification conditions with varying amounts of alloying elements. From this research it will be possible to manufacture aluminum alloys using different alloying elements.

These can provide important information about the influence of alloying elements on the microstructure and mechanical properties. First it describes aluminum alloys, classification of aluminum alloys, effects of major and minor alloying elements on aluminum alloys, aluminum-copper phase diagram, homogenization of aluminum alloys, CALPHAD modeling software, hardening techniques: equilibrium and Scheil-Gulliver, plastic hardening and deformation. work strengthening.

LITERATURE REVIEW

• Aluminum Alloys
• Classification of Aluminum Alloys
• Cast alloys
• Silicon
• Copper
• Magnesium
• Iron
• Manganese
• Nickel
• Zinc
• Lead
• Titanium
• Strontium
• Sodium
• Lithium
• Effects of Alloying Elements on Cast Aluminum Alloys
• Major Elements .1 Silicon
• Minor Elements .1 Nickel
• Microstructure Modifying Elements .1 Titanium and Boron
• Impurity Elements .1 Iron
• Solidification of Aluminum Copper Alloys
• Micrographs: Eutectic Alloy
• Micrographs: Hypoeutectic Alloy

Silicon is primarily responsible for the so-called “good castability”; that is, the ability to easily fill molds and solidify castings without hot cracking or hot cracking problems. They tend to solidify gradually from the mold surface toward the thermal center of the casting cross-section. These elements (one or the other, and not in combination) are added to eutectic or hypoeutectic aluminum-silicon casting alloys to modify the morphology of the eutectic silicon phase.

An RLM micrograph (Figure 2.10) of a 25%Cu/75%Al sample shows primary Al dendritic arms (white). The relative amounts of the two phases (Al and θ) in the eutectic are determined using the lever rule at the eutectic temperature [12].

Figure 2.1: Illustration of grain-refined aluminum by Titanium and Boron [10].

Cu Phase

• Heat Treatment of Aluminum Alloys
• Thermodynamic Modeling of Phases .1 CALPHAD Description
• Calculation of Phase Diagram
• Thermodynamic Databases
• Modelling Software Packages
• Non-equilibrium Solidification
• The Scheil-Gulliver (SG) Solidification Model
• Plastic Deformation and Work Hardening
• Scope of the Current Work

The basic principle of thermodynamic equilibrium calculation is the minimization of the total Gibbs energy of the system (Figure 2.15) [19]. The CALPHAD method is based on the fact that a phase diagram is a representation of the thermodynamic properties of a system. The roots of the CALPHAD approach lie in the mathematical description of the thermodynamic properties of the phases of interest.

However, they are all based on predicting the properties of the higher-order system from lower-order systems. For calculations, this software relies on the physical properties of the material rather than statistical methods. As the temperature decreases, the solid solution continues to grow at the expense of the liquid.

However, diffusion will take place and all the solid solution will have uniform composition M2, which is the total composition of the alloy. As the temperature decreases, the average composition of the solid solution will deviate further from equilibrium conditions. At this temperature, the composition of the solid solution M3 coincides with the alloy composition, and solidification is complete.

Where k is the partition coefficient and Co is the composition of the original liquid alloy. Eventually the composition of the liquid will reach the eutectic composition and final solidification will occur via this reaction. Taking into account the dependence of the creation rate of dislocations on τ, the creation rate can be written as.

Figure 2.13: Hypereutectic Al-Cu alloy (RML) [12].

EXPERIMENTAL PROCEDURES

• Material
• Alloy Preparation
• Wet Chemical Analysis of As Cast Alloys
• Homogenization Treatment of As-Cast Aluminum Alloys
• Deformation of Homogenized Alloys
• Determination of Phases Present in the Microstructure
• Energy Dispersive X-Ray (EDX)
• Differential Thermal Analysis (DTA)
• Image Analysis
• Mechanical Property Determination

The melt was mixed again and the temperature of the entire melt was measured with a thermocouple. For each alloy, at least four sparks were produced at different casting locations and the average composition was determined. The area under the DTA peak is the enthalpy change and is unaffected by the heat capacity of the sample.

Shading correction was required during optical microscope image collection; otherwise the image analysis would not give accurate results. An upper threshold was set for the first image of the sample before starting the measurements. If it was found that most of the images were not well distinguished, the threshold value was changed to match most of the images.

Erosion operation removes pixels from the edge of the black object; it simply means that the size of the objects that are darker than the background (eg black phases after thresholding) is reduced. On the other hand, dilation adds pixels to the edges of the black objects (thus increasing the size of the objects darker than the background). Before starting the measurement, an option was selected so that the calculation would include edges of the image.

Segmenting just one particular phase is mostly impossible because most phases have similar color and shape. Then during segmentation only that phase, the value of the lower and upper threshold was chosen to be 255 and 255 so that only the white parts of the image are thresholded. For each as-cast and homogenized state alloy hardness and also under 10%, 20% and 50% deformed state were measured on the HRF scale at different locations of the sample.

Table 3.1: Alloy designation of Al-Cu-Mg alloys used in the current work

RESULTS AND DISCUSSION

• Chemical Analysis
• Significant Phases of Al-Cu-Mg Alloys .1 Phases Predicted

During non-equilibrium cooling, no additional phases were formed compared to equilibrium cooling condition for the same composition of alloy A1. The phase silicon which was very negligible in the equilibrium cooling condition completely disappeared in non-equilibrium cooling. The phase silicon which was very negligible in equilibrium cooling completely disappeared in non-equilibrium cooling.

The silicon and Al5Cu2Mg8Si6 phases were very negligible under equilibrium cooling and completely disappeared under non-equilibrium cooling. During equilibrium solidification, significant phases are formed: Al7Cu2M, Al2CuMg, Mg2Si and Al2Cu (Figure 4.11). During equilibrium solidification, significant phases are formed: Al7Cu2M, AlFeSi, Silicon and Al2Cu (Figure 4.13).

During non-equilibrium cooling, only two significant phases were formed for the same C0 alloy (Figure 4.14). Silicon and AlFeSi phase that were very negligible in equilibrium cooling have completely disappeared in non-equilibrium cooling. During equilibrium solidification, the important phases formed are Al7Cu2M, AlFeSi, Silicon and Al2Cu (Figure 4.15).

Under non-equilibrium cooling conditions, only two significant phases were formed for the same composition of alloy C1. Phase silicon and AlFeSithose were very insignificant in equilibrium cooling have totally disappeared in non-equilibrium cooling. During equilibrium solidification, significant phases Al7Cu2M, Al2CuMg, Mg2Si and Al2Cu are formed (Figure 4.17).

Figure 4.1: Change in fraction solid wt % with temperature of alloy A0 (EQM).

Cu 2 M Phase

Table 4.7 also shows that this phase only forms in alloys with a low copper content.

CuMg Phase

• Effect of Magnesium on Phase Fraction
• Effect of Alloy Addition in Solidus and Liquidus Temperature
• Determination of Homogenization Temperature
• Microstructure
• Effects of Homogenization Treatment
• Phases Observed
• Deformation of Homogenized Aluminum-Copper-Magnesium Alloys
• Effect of Deformation on Microstructure
• Effect of Chemical Composition on Microstructure
• Effect of Solution Treatment
• Effect of Solution Treatment on Microstructure
• Effect of Chemical Composition on Hardness
• Effect of Deformation on Hardness
• Effect of Solution Treatment on Hardness
• Processing Parameters that Dominates Hardness in Aluminum Copper Magnesium Alloys

From Figure 4.66, it can be observed that the effect of magnesium was more significant compared to copper. From Figure 4.68, it can be observed that the effect of copper was more significant compared to magnesium. From Figure 4.69, it can be observed that the effect of copper was more significant compared to magnesium.

Figure 4.71 shows that the effect of magnesium was more significant than that of copper. Figure 4.72 shows that the effect of magnesium was much greater than that of copper. Figure 4.74 shows that the effect of magnesium was much greater than that of copper.

It can be seen from Figure 4.75 that the effect of magnesium was much greater compared to copper and deformation. It can be seen from Figure 4.76 that the deformation effect was much greater compared to copper and magnesium. It can be seen from Figure 4.77 that the effect of magnesium was greater compared to copper and deformation.

From Figure 4.78 it can be observed that the effect of magnesium was more significant compared to copper and deformation. From Figure 4.80 it can be observed that the effect of magnesium was more significant compared to deformation and copper. From Figure 4.81 it can be observed that the effect of magnesium was more significant compared to deformation and copper.

From Figure 4.82 it can be observed that effect of deformation was much more significant compared to copper and magnesium. From Figure 4.83 it can be observed that the effect of magnesium was more significant compared to deformation and copper.

Table 4.9: Weight fraction of Mg 2 Si phase at 200°C.

CONCLUSION

Deformation also changes the microstructure by destroying the necklace shape of the Al-Cu-Mg phases. For this reason, with a larger deformation, the increase in hardness may not be very significant. ix) Solution treatment at 500 °C results in a decrease of the phase fraction in the microstructure compared to that without any solution treatment. The addition of copper results in an increase in the hardness of the homogenized aluminum-copper-magnesium alloy. xi) Solution treatment also reduces the hardness of aluminum alloys due to the dissolution of Al2Cu and Mg2Si phases in the aluminum matrix. xii) ANOVA modeling concludes that magnesium addition and amount of deformation affect the strength of Al-Cu-Mg alloys to a greater extent compared to copper addition and homogenization treatment.

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APPENDIX A