Partitioned matrices back to array

mat1 = Table[    If[i > j, RandomReal[], -RandomReal[]], {i, 16}, {j, 16}];  mat2 = Partition[mat1, {4,4}]; 

Is there a possibility to get the first one from the second one. I have a form as in mat2 ie, as partitioned matrices. Can I get the form as in mat1 ie, 16 X 16? When I use flatten, the issue is like it’s changing the place of terms.