Istraživanje efekta ojačavanja starenjem tokom termomehaničke obrade aluminijumskih legura

Abstract

Ova doktorska disertacija obuhvatila je istraţivanja na aluminijumskim legurama iz serije 6000 (Al-Mg-Si legure, komercijalne aluminijumske legure EN AW-6060 i EN AW-6082). Na pomenutim legurama sprovedena je različita termomehanička obrada, nakon čega je ispitivan uticaj reţima prerade na mehanička, fizička, toplotna i strukturna svojstva. Ispitivanja su raĎena u cilju karakterizacije ispitivanih legura i sagledavanja uticaja prisutnih legirajućih elemenata (hemijskog sastava) na njihove strukturne, mehaničke, fizičke i toplotne karakteristike čime je dat i odreĎeni naučni i stručni doprinos boljem poznavanju ispitivanih Al-Mg-Si legura nakon starenja (prirodnog i veštačkog), kao i nakon termomehaničke obrade koja je sprovedena u cilju proučavanja njenog uticaja na efekat ojačavanja starenjem. Ciljevi istraţivanja usmerili su ovu disertaciju tako da doprinese boljem poznavanju uticaja reţima primenjene termomehaničke obrade na strukturu i osobine ispitivanih Al-Mg-Si legura, što će uz nesumnjiv teorijski doprinos omogućiti i proširenje njihove primene u najsavremenijim industrijama, gde je trenutno velika potraţnja za materijalima sa aluminijumskom osnovom sa poboljšanim osobinama. Doktorska disertacija je podeljena u osam poglavlja. U uvodnom delu dat je kratak osvrt na veliku potraţnju u industriji u poslednjim decenijama za materijalima koji po odreĎenim osobinama mogu zameniti materijale iz oblasti crne metalurgije, s obzirom na to da njihova proizvodnja iziskuje veliku potrošnju energije i dovodi do zagaĎivanja ţivotne sredine, kao i na ulogu aluminijuma i njegovih legura u ovom domenu. Osnovne napomene o aluminijumu i legurama na njegovoj osnovi, uz kratak osvrt na primenljivost ovih legura u industriji, kao i kratak opis uticaja postupaka prerada na strukturu i karakteristike aluminijuma i njegovih legura prikazan je u drugom poglavlju. U trećem poglavlju opisane su osnovne teorijske postavke i uslovi za pojavu precipitacionog ili taloţnog ojačavanja (ojačavanja starenjem), kao jedne od najčešće korišćenih metoda za poboljšanje osobina kod aluminijumskih legura, pa i kod Al-Mg-Si legura. U četvrtom poglavlju predstavljeni su postojeći publikovani rezultati o karakterizaciji legura sistema Al-Mg-Si. Ciljevi istraţivanja prikazani su u petom poglavlju. U šestom poglavlju opisan je način izvoĎenja eksperimenata i dat je uvid u metode kojima je moguće izvršiti potrebna merenja i karakterizaciju dobijenih uzoraka. Za karakterizaciju legura korišćeno je više savremenih, standardizovanih metoda i tehnika. Eksperimetalni rezultati svih izvršenih ispitivanja sistematizovani su i izneti u sedmom poglavlju ovog rada uz odgovarajuću analizu i diskusiju rezultata. Legure EN AW-6060 i EN AW- 6082 dobijene su od strane „Al-Cu metali― firme iz Niša u obliku flahova i izraĎene su po standardima koji diktiraju parametre izrade. Kompletan materijal je podvrgnut ţarenju radi uklanjanja fabričke strukture i dobijanja najmekšeg stanja (temper O). Ovo ţarenje je uraĎeno na temperaturi od 550°C u trajanju od 6 h. Nakon uklanjanja fabričke strukture, izdvojeni su uzorci u setove i svaki od setova je bio podvrgnut različitoj termičkoj ili termomehaničkoj obradi. U prvom setu cilj je bio dobijanje početnih uzoraka koji su korišćeni za poreĎenje, stoga je grupa uzoraka podvrgnuta rastvornom ţarenju u trajanju od 1 h na temperaturi od 550°C i kaljenju u vodi sa ledom radi dobijanja presićenog čvrstog rastvora (temper W). Zatim je pristupljeno isptivanju parametara koji definišu precipitaciono ojačavanje (starenje). U ovom setu ispitivan je uticaj temperature rastvornog ţarenja, pa su stoga uzorci podvrgavani različitim temperaturama rastvornog ţarenja (510°C, 530°C, 550°C, 570°C, 590°C), nakon čega su uzorci ispitivani odmah nakon kaljenja, nepotpunog starenja i potpunog starenja...

This doctoral dissertation included the investigation of aluminium alloys from 6000 series (Al-Mg-Si alloys, commercial aluminium alloys EN AW-6060 and EN AW-6082). Various thermomechanical treatments (TMT) were applied to these alloys, after which the influence of these regimes on the mechanical, physical, thermal and structural properties was examined. The investigations were performed in order to characterize the alloys and to investigate the influence of alloying elements (chemical composition) on structural, mechanical, physical and thermal properties. These investigations also gave a certain scientific and professional contribution to better understand the investigated Al-Mg-Si alloys after ageing (natural or artificial), as well as after the thermomechanical treatment that was applied in order to study its effect on the precipitation hardening process. The research aim in this doctoral dissertation was to contribute to a better understanding of the influence of applied thermomechanical treatment on the structure and properties of the investigated Al-Mg-Si alloys. This will undoubtedly give the theoretical contribution and the expansion of the use of these alloys in modern industry, where currently there is a high demand for aluminium-based materials with improved properties. The doctoral dissertation is divided into eight chapters. The introductory section gives a brief overview of the great demand in the industry for materials that can replace materials in the field of ferrous metallurgy, since the production of ferrous metals requires high energy consumption and leads to environmental pollution, as well as to the role of aluminium and its alloys in this domain. Basic notes on aluminium and its alloys, with a brief overview of the applicability of these alloys to the industry, as well as a brief description of the impact of processing operations on the structure and characteristics of aluminium and its alloys, are presented in Chapter Two. The third chapter describes the basic theoretical assumptions and conditions for the appearance of precipitation hardening or ageing as one of the most commonly used methods for improving the properties of aluminium alloys including the Al-Mg-Si alloys. Chapter 4 presents the published results on the characterization of Al-Mg-Si alloys. The research goals are presented in Chapter Five. The sixth chapter describes the method of performing the experiments and gives an insight into the methods that can be used to perform the necessary measurements and characterization of the obtained samples. Several modern, standardized methods and techniques have been used to characterize the alloys. The experimental results of all the tests performed are systematized and presented in the seventh chapter of this paper with appropriate analysis and discussion of the results. The alloys EN AW-6060 and EN AW-6082 were produced and delivered by the company ―Al-Cu metali‖ in the form of rectangular bars. All necessary standards that dictate the manufacturing parameters were followed during the production. The received material was subjected to annealing to remove the fabricated state and to obtain the lowest strength and highest ductility (temper O). This annealing was done at a temperature of 550°C for a period of six hours. After obtaining adequate temper, the bars were cut to the appropriate dimensions and the samples of both alloys in this state were separated to be subjected to different HT or TMT. Firstly, the goal was to obtain the initial samples which would later be used for comparison in every other experiment. The samples of both alloys were subjected to solution heat treatment at 550°C and then quenched in ice water in order to obtain a super saturated solid solution (αssss) (temper W). After that, investigation of the parameters that define the ageing treatment was started. In this set of samples, the influence of the solutionizing temperature was examined, and in this setsamples were subjected to different solutionizing temperatures (510°C, 530°C, 550°C, 570°C, 590°C), where the samples were examined immediately after quenching, after partial ageing and after complete ageing. Results of these experiments were later used as a guide in defining the optimal solution heat treatment temperature.