Zaostale napetosti v zvarih na aluminijevi zlitini 7075

Avsenik, Rok (author), Klobčar, Damjan (mentor), Trdan, Uroš (comentor)

Zaostale napetosti so izredno pomembne iz vidika obratovalne dobe strojnega dela, saj so prisotne v materialu tudi takrat, ko nanj ne deluje nobena zunanja obremenitev in so posledica različnih proizvodnih procesov kot je litje, varjenje, preoblikovanje, toplotne obdelave itd. Napetosti lahko v splošnem razdelimo kot tlačne in natezne. V diplomski nalogi smo merili zaostale napetosti v varih na aluminijevi zlitini 7075, zvarjeni po postopku varjenja z gnetenjem. Vzorci so bili zvarjeni z orodjem iz orodnega jekla in s parametri 950 in 750 vrt/min, ter podajanji 73, 93 in 116 mm/min. Zaostale napetosti smo merili z metodo rentgenske difrakcije (ang. X-ray difraction - XRD) na mestu varjenja in toplotno vplivnem območju (TVO). Na velikost zaostalih napetosti v največji meri vpliva delež vnesene toplote. V primerjavi z drugimi postopki varjenja ima postopek varjenja z gnetenjem manjši linijski vnos toplote in posledično lahko pričakujemo manjše vrednosti zaostalih napetosti. Ugotovili smo, da se zaradi varjenja z gnetenjem v območju zvara in TVO, pojavijo natezne zaostale napetosti, kot posledica vnosa toplote in deformacij med varjenjem z gnetenjem. Toplota in deformacije privedejo do sprememb v mehanskih lastnostih materiala. Zvari z višjimi nateznimi zaostalimi napetostmi se odražajo z višjo trdoto, ter nižjo natezno trdnostjo.

• Language: Slovenian
• Keywords: Merjenje zaostalih napetosti, varjenje z gnetenjem, parametrična analiza, aluminijeva zlitina 7075, rentgenska difrakcija
• Work type: Bachelor thesis/paper
• Typology: 2.11 - Undergraduate Thesis
• Organization: FS - Faculty of Mechanical Engineering
• Publisher: [R. Avsenik]
• Year: 2018
• PID: 20.500.12556/RUL-103769
• UDC: 53.08:621.791:669.715(043.2)
• COBISS.SI-ID: 16234779
• Publication date in RUL: 25.09.2018

Secondary language

• Language: English
• Title: Residual stresses in welded aluminium alloy 7075

Abstract

Residual stresses are extremely important in terms of the operating life of the machine part, since they are present in the material even when there is no external force and are the result of their manufacture processes such as casting, welding, forming, heat treatments, etc. Residual stresses can generally be divided as tensile or compressive. In our work we measured the residual stresses in friction stir welded aluminium alloy 7075. The samples were welded with a tool made of hot work tool steel and with parameters 950 and 750 rpm, and welding speeds 73, 93 and 116 mm / min. The residual stresses were measured using the X-ray diffraction methodology across the whole weld and heat affected zone. They were measured in longitudinal and transversal direction of the weld face. The amount of residual stresses is mostly affected by the heat input. In comparison with other welding processes, friction stir welding has a smaller linear heat input, and lower residual stresses values can be expected. We found out, that due to friction stir welding in the weld area and in the HAZ, tensile residual stresses occur. Residual stresses occur as a result of heat and deformation, during friction stir welding. Due to heat and deformation, there are changes in mechanical properties. Welds with higher tensile residual stresses have higher hardness and lower tensile strength.

• Keywords: Measurement of residual stresses, friction stir welding, parametric analysis, aluminium alloy 7075, X-ray diffraction