Context : Recent observational results have demonstrated an increase in the surface Na abundance that correlates with stellar mass for red giants between 2 and 3 M _ { \odot } .
This trend supports evolutionary mixing processes as the explanation for Na overabundances seen in some red giants .
In this same mass range , the surface Al abundance was shown to be constant .

Aims : Our main aim was to extend the investigation of the Na and Al surface abundances to giants more massive than 3 M _ { \odot } .
We sought to establish accurately whether the Na abundances keep increasing with stellar mass or a plateau is reached .
In addition , we investigated whether mixing can affect the surface abundance of Al in giants more massive than 3 M _ { \odot } .

Methods : We obtained new high-resolution spectra of 20 giants in the field of 10 open clusters ; 17 of these stars were found to be members of 9 clusters .
The giants have masses between 2.5 M _ { \odot } and 5.6 M _ { \odot } .
A model atmosphere analysis was performed and abundances of up to 22 elements were derived using equivalent widths .
Additionally , abundances of C , N , and O were determined using spectrum synthesis .
The abundances of Na and Al were corrected for non-local thermodynamic equilibrium effects ( non-LTE ) .
Moreover , to extend the mass range of our sample , we collected from the literature high-quality C , N , O , and Na abundances of 32 Galactic Cepheids with accurate masses in the range between 3 M _ { \odot } and 14 M _ { \odot } .

Results : The surface abundances of C , N , O , Na , and Al were compared to predictions of stellar evolution models with and without the inclusion of rotation-induced mixing .
The surface abundances of most giants and Cepheids of the sample can be explained by models without rotation .
For giants above \sim 2.5 M _ { \odot } , the Na abundances reach a plateau level of about [ Na/Fe ] \sim 0.20-0.25 dex ( in non-LTE ) .
This is true for both Cepheids and giants in open clusters .
Regarding Al , the non-LTE [ Al/Fe ] ratios are mostly close to solar and suggest that Al is not affected by the first dredge-up up to \sim 5.0 M _ { \odot } .
Our results support previous works that found models with rotation to overestimate the mixing effects in intermediate-mass stars .

Conclusions :