Evaluation of the diploma thesis – opponent
Opponent: doc. Ing. Kateřina Skotnicová, Ph.D.
Subject matter: Casting Aluminum Alloys for Automotive Student: José Sena
1. Meeting the requirements of the thesis assignment.
The diploma thesis corresponds to the assignment in full.
2. Thesis technicality evaluation.
The individual chapters and subchapters follow each other logically and factually. The findings and information given in the theoretical part of the work are fully related to the experimental part. The text is written in readable form, with only minor grammatical mistakes. However, I am not competent for a deeper assessment of the level of the English language.
3. Results evaluation of the thesis.
The total range of the diploma thesis is 60 pages. The theoretical part of the thesis summarizes the basic knowledge about 3xx aluminum alloys (Al-Si, Al-Si-Mg, etc.), the conditions of their heat treatment, the possible defects and the influence of additives and admixtures on their properties. This section concludes with a description of the casting technologies of these alloys. I have no comments on the theoretical part, which is very clear.
The main aim of the experimental part of the thesis was the characterization of microstructure and properties of three different castings of aluminum alloys – AlSi7Mg alloy (Samples 1, 2 and 3), AlSi12 alloy (Sample 4) and AlSi10Mg alloy (Sample 5). The three different aluminum profiles from the 1xx family were also studied. This part of the work shows some formal shortcomings:
Methods (techniques) used for the analysis of structural characteristics and chemical composition of samples, as well as the procedure of preparation of metallographic samples are not described. It is also not specified from which part of the castings the samples were cut for further study.
Instruments used for the study are not specified.
References to figures in the text are almost always given after their placement. In some sections, the reader must return 4 pages to find out which image it is (e.g. Fig. 6.50). References to tables are not given at all. Figures and tables are described very generally – e.g. Table 6.1 Chemical analysis, Fig. 6.10 Sample 1.
Abbreviations used in the thesis are not explained.
Some of the achieved results are not commented, e.g. the values of porosity and microhardness.
4. Evaluation of the new finding’s contribution.
The graduate states that a new intermetallic phase with the stoichiometric formula Al12Si9Sr4 was found in the structure of AlSi7Mg alloy (Sample 1). However, this finding should be further confirmed by a more
appropriate method. The presence of the intermetallic phase based on Al-Mn-Fe-Si in the structure of Sample 2 is also interesting.
5. Utilization and selection of information sources.
The literature search of the solved problem was performed in detail. All used articles and other literature are properly cited in the text.
6. Questions for the defense of the thesis.
I would like to ask the graduate to answer the following questions:
a) Which casting technology was used to produce the individual alloys (castings)?
b) The color etching was also used to study the microstructure of samples. What does this procedure include and what are its benefits?
c) There is given in the subchapter 6.1.6 that a new intermetallic phase with the stoichiometric formula Al12Si9Sr4 was found in the structure of AlSi7Mg alloy. Is this really an intermetallic compound unknown yet? Could the composition of this phase not be influenced by its surroundings? Which method(s) could you use to accurately identify this phase?
d) The Al-2 and Al-3 samples have almost identical chemical composition and grain size. How could you explain the difference in their microhardness?
e) Chapter 6.1.4 characterizes defects in the structure of AlSi7Mg (A356) alloy. Which method was used to evaluate the porosity of samples 1 to 3?
7. Summary evaluation.
The obtained results could be published in the professional journals. The diploma thesis meets all the requirements for its elaboration, and I recommend it for defense before the state final exam commission.
Overall assessment: Excellent
Ostrava 22th June 2020
Venue: ______________________, date: ___________ ______________________
opponent’s signature
