No! Sand and clay can make cement. What you need is some organic matter to mix with the sand and then add this to the clay soil. You can buy bags of compost from any garden center and if you mix that one and one with the sand you'll have great soil to add on top of your lawn or dig into the garden beds. Don't want to buy two yards of compost? Just move the sand to a corner, cover with a tarp to keep it dry and weed free and then take your time mixing it with compost or peatmoss or steer manure and then adding this mix to your clay soil. Better to do a little bit over time. Another option is to aerate your lawn, add one inch of compost or topsoil raked all over the lawn and then spread two inches of sand on top of this. Then the worms will the mixing for you but the sand will not be in contact with the clay.