We have no evidence that the Israelites were ever enslaved in Egypt. In the book the Bible Unearthed, Israel Finkelstein and Neal Asher Silberman state the following:
We have no clue, not even a single word, about the early Israelites in Egypt: neither in monumental inscriptions on the walls of temples, nor in tomb inscriptions, nor in papyri. Israel is absent - as a possible foe of Egypt, as a friend, or as an enslaved nation.
We have an Egyptian monument from 1208 BCE which states that "Israel is laid to waste", however this simply confirm the existence of Israelites living in Canaan and does not mention the enslavement or the exodus out of Egypt.
The Hyksos connection
Josephus the 1st century Jewish historian, wrote that the exodus was connected to the expulsion of the Hyskos out of Egypt. Some Christians use this quote to prove that the Israelites were indeed in Egypt however it is much more likely that the early Canaanites adopted the Hyksos story as their own (see question 'Who were the Hyksos people?')
The Habiru inscription
There exists a cuniform tablet which was written by the Egyptians in the 14th century BCE. In it they describe a people called the Habiru people. Initially some scholars claimed that this was a reference to the Hebrews and finally evidence that the Hebrews were indeed slaves in Egypt. Since this discovery we have found references to the Habiru or Apiru as some called them in various Sumerian, Akkadian, Mitanni, Hittite and Ugaritic sources.
Depending on the context the Habiru were generally considered a nomadic group of outlaws, thieves, rebels, slaves or migrant workers. They are considered to be a middle eastern form of gypsies. They were a melting pot of people who had fallen out of step with their societies and were generally considered to be a nuisance wherever they went.
But Israelites they were not.