It looks like it was really fried on that hot day.I'd take it out of the full sun for awhile,not complete shade,kind of dappled light if possible and gradually give more light. What's the potting mix? Brady

You always need to be more careful with moisture retaining soils. Large Mangos are quite tough plants and will often come back from severe reversals. Smaller trees are more sensitive. They've evolved in a monsoonal climate where they often get flooded out during the wet season and are completely dry in the dry season. The dry season coincides with the coolest night time temperatures. A wooden skewer or chop stick pushed into the soil to see if there's moisture below is a common method for checking. The surface soil will often look dry when below it isn't. The leaves in your second photo are okay, but don't let them get to the stage of those in the first photo. And keep them away from cold night temperatures.

Looks like a root rot problem. But A) we can't see the entire plant and B) we have no way to check the soil.

I stop fertilizing when temps rise above 80-85*. High temps make roots and the above ground parts of plants very lethargic when they need water most. How readily water moves into cells depends on the level of solutes within the cell. The higher the level of solutes in the cell, the easier it is for water to pass through the semi-permeable cell membrane and into the cell. Conversely, the lower the level of solutes in the soil solution (free water in soil), the easier the cell solution passes the membrane into the cell. For a high % of terrestrial plants other than cacti, root function begins to drop off at root/soil temps of about 80*. If the pot is shaded, root/soil temps usually lag ambient air temps by 10-15*F due to evaporative cooling, so as long as the soil is moist, air temps in shade would need to be in the mid 90s before there was a serious issue with root function. In full sun pounding the pots, soil temps can be much higher - at least 15* higher than ambient air temps in most cases, though that varies too with soil moisture levels and air movement. High root temps are a stealthy attacker. Most often, you won't even realize the damage done to roots (especially trees) on the sunny side of the pot until late fall or even early spring when branches on what was the sunny side of the tree start dying and root rot becomes an issue to deal with. So to be safe, I stop fertilizing at 80*F which facilitates water uptake and movement in the plant. That is also why I try to use controlled release fertilizers sparingly. Their release rate is driven primarily by temperature, so when temperatures reach the point where you want to pull back on the level of salts in the soil solution, controlled release fertilizers will have rendered the grower with no control other than trying to scrape the fertilizer prills off of the top of the soil. I like and feel as though I need the control over nutrition offered by synthetics like Foliage-Pro 9-3-6 in order to achieve the best results. I do use Osmocote-Plus sparingly for younger plants which need to develop more mass before they are started along the path to becoming a bonsai, but not on the trees which are in the stage where I have started developing finer branching and am reducing leaf size. That and beyond is when control is most important. For other hobby growers not saddled with the concerns that come with bonsai, it's simply trying to make it easier for the plant to get water when it needs it most. Al