It is not that simple...
For the sake of simplicity, let`s put aside "Intermediate" flutes and just look at "Student" and "Professional" flutes.
Student flutes are almost always silver plated, over a metal similar to that used for coins, called "nickel silver", (although it contains no silver!) The plating is to make it look nice, and resist unsightly corrosion.
Professional flutes normally have a higher standard of design and manufacture, The higher standard of manufacture may make them more reliable. The higher standard of DESIGN makes them play better.
In spite what teachers and manufacturer`s advertising BS may tell you, the actual metal has an almost irrelevant effect on how the flute plays. This has been established in scientific (double blind) testing.
For one such research, see (at least the summary) at
http://iwk.mdw.ac.at/Forschung/english/linortner/linortner_e.htm
Flute players have been duped into BELIEVING that the metal is very important for how a flute plays, but it is DESIGN that is important. The reason for this deception is partly so that manufacturers can charge enormous sums for instruments that do not cost a lot more to make. And they get away with it.
ALMOST always, a reputable maker of professional instruments will make the flute (the tubing at least) from silver or a precious metal. But that is almost entirely for marketing reasons.... After all, a maker will not sell many if he charges megabucks for a flute made from stainless steel, even though it would be much more difficult to make from stainless steel than silver or gold.
So it is the minds of players, copying the marketing image of the likes of James Galway, who have created this aura about using precious metals for flutes.
To complicate things, it is very easy for people to deceive their own minds. If we BELIEVE something is true, then it is difficult to convince us that it is not. This is amply demonstrated in peoples` religious attitudes. So if you BELIEVE that a silver or gold flute will play better, then it you will very likely MAKE it play better - especially if you payed megabucks. And the manufacturers just love this phenomenon. It provides the opportunity to make a LOT of money!
Note that precious metals are almost NEVER used for other woodwinds. Note also that silver is actually not that expensive. Gold costs about 300 times more.
And it gets more complicated....
SOME manufacturers have more or less specialised in the bulk market - STUDENT flutes. If you get a rather roughly-designed student flute and make the same inferior design out of silver, you get a flute that DOES NOT PLAY ANY BETTER than the student version. Yet these manufacturers are conning many people otherwise, capitalising on the player`s beliefs and capacity for self deception.
So the preoccupation in this forum with what instruments are made from, and the assumption that this is the all-important issue, is very misleading.
If you want a good student flute, you go for a manufacturer with a reputation (among people who are WELL-familiar with many models of student flute) for making good student flutes.
If you want a professional standard flute, you don`t head for any flute that is solid silver or gold. yOu head for a MANUFACTURER who has a reputation for making flutes that are superb to play, i.e. you head for what is being used by professional players, and you will get names like Muramatsu, Powell, Altus, Mateki, (and many more). You find a design that happens to suit you - and your wallet! BTW very few professionals would be playing Gemeinhardts.
So, in short, a top quality flute is almost certain to be made for solid silver or other precious metal, but it probably did not NEED to be in order to be a great flute. And just because a flute is solid silver does NOT mean it is a great flute. We do not need to go to Chinese instruments to have this demonstrated!
BTW, "solid silver" usually refers to "sterling Silver", which is defined as at least 92.5% pure silver. (100% pure silver is too soft)
And also possibly of interest, even sterling silver flutes are often silver (+ rhodium?) plated, for a better appearance or more corrosion resistance.
So, stop focusing on features and metals, and instead, focus on standard of design and manufacturer. On these issues you can believe almost nothing from manufacturers. You have to rely on reputation, unless you have access to alternative thorough and reliable evaluation.
Definitely do not believe much of what you hear or read from student players, marketers, and unfortunately a good proportion of teachers and band directors, who often have no idea of how much they don`t know! Also, try to get beyond the `BELIEF` systems described earlier.
