BWA aln provides -I option that can be used to align fastq reads with Phred+64 quality scores. The reads in output bam file have base quality in Sanger or Phred+33 format. BWA-mem doesn't have that option (at least not stated in the manual). If you search on this forum there are multiple posts that explain in detail about how to test if reads belong to Phred+33 or Phred+64. Also, you can easily convert them from one to other. Base quality scores are not used in the calculation of mapping quality scores but BWA mem may throw an out of range error if it can't take Phred+64 fastq files.