can you just use either Min or Max

because your summing sql server is converting to an int and giving you a number......

if you need sum then

Select

case fri when 0 then space(2) else right('00' + convert(varchar(2),fri),2)

case sat when 0 then space(2) else right('00' + convert(varchar(2),sat),2)

case sun when 0 then space(2) else right('00' + convert(varchar(2),sun),2)

case mon when 0 then space(2) else right('00' + convert(varchar(2),mon),2)

case tue when 0 then space(2) else right('00' + convert(varchar(2),tue),2)

case wed when 0 then space(2) else right('00' + convert(varchar(2),wed),2)

case thu when 0 then space(2) else right('00' + convert(varchar(2),thu),2)

from (

select

SUM(CASE WHEN datepart(dw,t_date+2) = 1 THEN a1 ELSE 0 END) as fr1,

SUM(CASE WHEN datepart(dw,t_date+2) = 2 THEN a1 ELSE 0 END) as sat,

SUM(CASE WHEN datepart(dw,t_date+2) = 3 THEN a1 ELSE 0 END) as sun,

SUM(CASE WHEN datepart(dw,t_date+2) = 4 THEN a1 ELSE 0 END) as mon,

SUM(CASE WHEN datepart(dw,t_date+2) = 5 THEN a1 ELSE 0 END) as tue,

SUM(CASE WHEN datepart(dw,t_date+2) = 6 THEN a1 ELSE 0 END) as wed,

SUM(CASE WHEN datepart(dw,t_date+2) = 7 THEN a1 ELSE 0 END) as thu

) as X