In response to everyone else, I'm happy to share, hopefully it will provide some level of assistance. The design and relative ease of access for maintenance is quite impressive.
I've been under a lot of cars and I think the robust aluminum under frame and suspension components show that Honda did not cheap out of this vehicle.
The Clarity frame employs six different grades of steel - SFAIK aluminum is used only in body panels (except the roof).
Take a look through the photos, there are copious amounts of aluminum used in the under frame, crossmember and suspension assemblies. There's another post on this forum just dedicated to the special 5 link aluminum rear suspension. Even the rear hub/knuckle is aluminum.
I guess I don't know what you mean by the term, "under frame". The largest amount of aluminum used is in the body panels, not in the frame. The only frame member that's aluminum is the engine-mount subframe. I realize that the suspension has aluminum componentry: There's this from Honda's Clarity Press Kit -
"The lightweight front suspension utilizes forged aluminum lower arms and hollow cast iron steering knuckles that are 10 percent lighter than conventional solid cast iron knuckles and the lower arms use liquid-filled bushings to minimize unwanted noise, vibration and harshness. All of the rear suspension arms are made of forged aluminum, achieving a 40 percent weight reduction versus a conventional steel design."
The front subframe is a one-piece, hollow die cast aluminum component offering a 20 percent weight reduction versus conventional designs. The technique was developed though Honda's experience in the development of hollow aluminum motorcycle frame components.
I'm still not sure if you've actually reviewed the photos, I've spent a lot of time under the car. You suggested that earlier that the only place aluminum was used was in body panels. What I'm trying to clarify is that there a bunch more very large assemblies which are made from aluminum besides the body panels. The largest one is the huge under frame (for lack of an official term, that's what I'm calling it) at the rear of the car which you can see part of in the rear wheel well. It is the main mounting for the entire rear suspension and also supports the fuel tank and AC charger. I've worked on a lot of cars and this is not at all common, usually assemblies this large are just steel.
And here's a little closer image of the rear suspension, which is almost entirely made of aluminum, including the hub itself
Furthermore, the front under body with a large portion of the engine subframe, the front controls arms and even the tie rod ends made of aluminum.
So, to my original point, aluminum is not just used in the body panels. Its extensively used in large and traditionally steel assemblies in the car. This would not be inexpensive to do, thus why its not common in vehicles in this price class. I've also spent some time looking into these assemblies on the same model year Insight everything I saw was traditional steel construction. In my opinion, this is impressive engineering and represents a good value to us as buyers. Especially so if you were able to purchase with the steep discounts that have been offered recently.