Optimizacija toplotne obdelave zlitine EN AW 6082 za nasadni ključ za gonilni ležaj : magistrsko delo

Fric, Jernej (author), Nagode, Aleš (mentor)

V okviru magistrskega dela smo izvedli optimizacijo toplotne obdelave zlitine EN AW 6082 za nasadni ključ za gonilni ležaj. Zlitina spada med toplotno utrjevalne, kjer se s procesom raztopnega žarjenja, gašenja in staranja (umetno ali naravno) dosežejo želene mehanske lastnosti materiala. Med staranjem se iz aluminijeve matice izločajo izločki, ki utrjujejo osnovo. Glavni cilj naloge je bil preučiti in predlagati najboljšo možno kombinacijo toplotnih obdelav skupaj s hladnim kovanjem nasadnega ključa iz zlitine EN AW 6082, za dosego zahtevanih mehanskih lastnosti (trdota in moment).Po homogenizacijskem žarjenju je bila izvedena toplotna obdelava T6 in T8, pri čemer smo vzorce starali različno dolgo časa na temperaturi 170 °C. Za mikrostrukturno karakterizacijo smo uporabili svetlobni in vrstični elektronski mikroskop (SEM), za dodatno pomoč pri določevanju faz ter izrisu diagramov pa smo si pomagali s programom Thermo-Calc. S programom Thermo-Calc je bilo ugotovljeno, da se zlitina začne strjevati pri temperaturi 650 °C in je v trdnem stanju pri temperaturi 551,3 °C. Pri sobni temperaturi so prisotne naslednje faze: Al3Ti, AlCuMgSi, silicij kot diamantna kubična struktura, Al13Cr4Si4, Al9Fe2Si2, Mg2Si, Al15Si2M4 in ?-Al. Mikrostruktura zlitine v F stanju je sestavljena iz primarnih kristalnih zrn faze ?, neravnotežnih evtektikov in kristalnih izcej po mejah kristalnih zrn. Homogenizacijsko žarjenje zlitine povzroči ogrobljanje faze Mg2Si ter abnormalno rast kristalnih zrn, spremeni pa se oblika intermetalnih faz iz ostrorobih v bolj ovalne. Pri zlitini v stanju F in O so prisotne naslednje faze: Mg2Si, Al(MnCrFe)Si in Al(MnFe)Si. Za zlitino v T6 stanju smo zahtevano trdoto 110 HB dosegli z umetnim staranjem na temperaturi 170 °C za 1 uro in 20 minut, za zlitino v T8 stanju pa smo to dosegli pri enaki temperaturi umetnega staranja vendar v času ene ure. Oba vzorca sta prestala preizkus vrtilnega momenta z zahtevanim minimalnim predpisom 50 Nm.

• Language: Slovenian
• Keywords: Zlitina EN AW 6082, toplotna obdelava, hladno kovanje, Thermo-Calc, mikrostrukturna karakterizacija, trdota.
• Work type: Master's thesis/paper
• Typology: 2.09 - Master's Thesis
• Organization: NTF - Faculty of Natural Sciences and Engineering
• Place of publishing: Ljubljana
• Publisher: [J. Fric]
• Year: 2021
• Number of pages: XVII, 52 f.
• PID: 20.500.12556/RUL-128351
• UDC: 669
• COBISS.SI-ID: 71663875
• Publication date in RUL: 09.07.2021

Secondary language

• Language: English
• Title: Heat treatment optimization of EN AW 6082 alloy for bottom bracket socket : master's thesis

Abstract

In the scope of this thesis, the heat treatment of the EN AW 6082 alloy for the bottom bracket socket was carried out. The alloy is precipitation hardable, where the desired mechanical properties of the material are achieved through the process of solution annealing, quenching and ageing (artificial or natural). During the process of ageing, due to precipitation the material hardness increases. The main aim of this thesis was to study and suggest the best possible combination of heat treatments together with cold forging of bottom bracket socket of an EN AW 6082 alloy, to achieve the required mechanical properties (hardness and torque). After homogenization annealing, heat treatments of T6 and T8 were carried out, whereby the samples were aged for different lengths of time at temperature of 170 °C. Scanning electron microscope (SEM) was used for microstructural characterization, and Thermo-Calc software for additional assistance in determing phases and plotting diagrams. With the Thermo-Calc software it was found that the alloy starts to solidify at 650 °C and is in a solid stare at a temperature of 551,3 °C. The following phases are present at room temperature: Al3Ti, AlCuMgSi, silicon as diamond cubic structure, Al3Cr4Si4, Al9Fe2Si2, Mg2Si, Al15Si2M4 and α-Al. The microstructure of the alloy in F temper consists of primary crystal grains of the α-phase, nonequilibrium eutectics, and microsegregations along the grain boundaries. Homogenization annealing of the alloy causes coarsening of the Mg2Si phase and abnormal growth of crystal grains, and the shape of the intermetallic phases changes from sharp-edged to more oval. The following phases are present in the F and O tempers of the alloy: Mg2Si, Al(MnCrFe)Si and Al(MnFe)Si. For the T6 temper, the required hardness of 110 HB was achieved by artificial ageing at 170 °C for 1 hour and 20 minutes, and for the T8 temper, this was achieved at the same artificial ageing temperature, but for 1 hour. Both samples passed the torque test with the minimum required regulation of 50 Nm.

• Keywords: EN AW 6082 alloy, heat treatment, cold forging, Thermo-Calc, microstructural characterization, hardness.