Gao, XudongLind, KarinAmarsi, Anish M.Buder, SvenDotter, AaronNordlander, ThomasAsplund, MartinBland-Hawthorn, JossDe Silva, GayandhiD'Orazi, ValentinaFreeman, KennethKos, JanezLewis, GeraintLin, JaneMartell, SarahSchlesinger, KatharineSharma, SanjibSimpson, Jeffrey D.Zucker, Daniel B.Zwitter, TomazDa Costa, GaryAnguiano, BorjaHorner, JonathanHyde, Elaina A.Kafle, Prajwal R.Nataf, David M.Reid, WarrenStello, DennisTing, Yuan-Senthe GALAH collaboration2019-12-192019-12-190035-8711http://hdl.handle.net/1885/196388Open cluster members are coeval and share the same initial bulk chemical composition. Consequently, differences in surface abundances between members of a cluster that are at different evolutionary stages can be used to study the effects of mixing and internal chemical processing. We carry out an abundance analysis of seven elements (Li, O, Na, Mg, Al, Si, and Fe) in 66 stars belonging to the open cluster M67, based on high resolution GALAH spectra, 1D MARCS model atmospheres, and non-local thermodynamic equilibrium (non-LTE) radiative transfer. From the non-LTE analysis, we find a typical star-to-star scatter in the abundance ratios of around 0.05dex⁠. We find trends in the abundance ratios with effective temperature, indicating systematic differences in the surface abundances between turn-off and giant stars; these trends are more pronounced when LTE is assumed. However, trends with effective temperature remain significant for Al and Si also in non-LTE. Finally, we compare the derived abundances with prediction from stellar evolution models including effects of atomic diffusion. We find overall good agreement for the abundance patterns of dwarfs and sub-giant stars, but the abundances of cool giants are lower relative to less evolved stars than predicted by the diffusion models, in particular for Mg.XDG, KL, and AMA acknowledge funds from the Alexander von Humboldt Foundation in the framework of the Sofja Kovalevskaja Award endowed by the Federal Ministry of Education and Research, and KL also acknowledges funds from the Swedish Research Council (grant 2015-004153) and Marie Skłodowska Curie Actions (cofund project INCA 600398). TZ acknowledges financial support of the Slovenian Research Agency (research core funding No. P1- 0188). SLM acknowledges support from the Australian Research Council through grant DE140100598. Parts of this research were conducted by the Australian Research Council Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D), through project number CE170100013.application/pdfen-AU© 2018 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society201810.1093/MNRAS/STY24142019-08-04