(Ⅰ)当a=0时,f(x)= -4x+2,x<- 1 2 4,- 1 2 ≤x≤ 3 2 4x-2,x> 3 2 ,∴由f(x)≥6,解得x≤-1,x≥2,∴不等式的解集是(-∞,-1]∪[2,+∞);(Ⅱ)∵|2x+1|+|2x-3|≥|2x+1-(2x-3)|=4,当且仅当2x+1=3-2x,即x= 1 2 取等号,∴要使不等式f(x)≥a2恒成立,则4+3a≥a2,解得:-1≤a≤4.