According to Taiwanese publication Economic Daily News, Apple intends to manufacture its next generation iPhones using 7000 series aluminum, an alloy that the company is already using for the Apple Watch. According to Apple, 7000 series aluminum is "60% stronger than most aluminum, and one-third the density of stainless steel." This type of alloy is also used to make competition bicycles.
Another thing that the next iPhones will reportedly borrow from the Apple Watch is the Force Touch technology, which enables a display to differentiate light touches from harder presses.
Apple will almost certainly announce (and launch) the iPhone 6s and iPhone 6s Plus in September. The handsets are expected to use new A9 chips (most of which will be manufactured by Samsung), while sporting displays similar to those found on the current models: 4.7 inches with 750 x 1334 pixels, and 5.5 inches with 1080 x 1920 pixels, respectively.
source: Economic Daily News (translated) via Mac Rumors