Titanium was supposed to make the iPhone Pro stand out from the competition, or at least that was the plan: Apple particularly highlighted the material during the presentation of the iPhone 15 Pro in September 2023: The construction with the high-quality metal is particularly light and yet stable. But the enthusiasm only lasted two years: the iPhone 17 Pro already used aluminum again. Recently, a leaker claimed that Apple would like to return to the ultra-light metal soon. Another voice now contradicts this: For technical reasons, Apple is, to a certain extent, condemned to using aluminum. A physical property apart from weight and resistance to deformation is crucial for the choice of material – its thermal conductivity. Titanium has a value of 22 W/(m*K) – a value approximately on par with stainless steel. Pure aluminum achieves 235 W/(m*K), so it dissipates excess heat ten times as quickly as the lighter titanium.
Thermal conductivity
| material | λ in W/(m*K) |
| mercury | 8.3 |
| stainless steel | 15 – 25 |
| titanium | 22 |
| zirconium | 22.6 |
| Aluminum oxide | 28 |
| Chrome steel | 30 |
| Brass | 120 |
| magnesium | 156 |
| aluminum | 236 |
| Gold | 314 |
| copper | 401 |
| Silver | 429 |
(Source: Wikipedia)
Aluminum is the best compromise
This makes aluminum currently the best compromise between durability, thermal conductivity, low weight and price. Only gold, copper and silver distribute the heat that occurs even faster. However, these are all significantly heavier, more expensive and not nearly as stable. Copper and silver would also oxidize noticeably quite quickly. Another innovation in the iPhone 17 Pro shows how important temperature regulation is: Apple integrated a steam chamber for the first time to quickly dissipate heat.
Oxide layer as an advantage
Aluminum is also covered by an oxide layer; However, this proves to be a stable protective layer against further corrosion. The electrolytic oxidation of aluminum is an extensively researched process that increases material stability. There are also various established methods for introducing color. That could be another reason to stay with aluminum: Apple took advantage of the return to aluminum in the iPhone 17 Pro to use a bright Cosmic Orange – an extremely popular color. At the same time, the oxide layer slows down heat radiation considerably; but at 28 W/(m*K), its thermal conductivity is still 27 percent higher than that of titanium.
Liquidmetal is still a dream of the future
Apple has been researching the use of Liquidmetal for many years; These are metal alloys in which no crystal structure forms. These use the element zirconium in large proportions and are said to have particularly advantageous properties; However, complex processing processes represent a major challenge. How the material behaves in terms of thermal conductivity is unknown; The main component zirconium has a value of 22.6 – as low as titanium.
