How to make qt 3d object transparent?

helloworld1

The example above shows how to create a wireframe view on top of the Trefoil .obj file. I want just the wireframe view. I have been trying to make the underlying .obj file transparent or make it disappear by setting the Alpha property of QPhongAlphaMaterial but am having no success. I'm actually doing this project in Qt 3D C++. The QML code translates line to line to C++.

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